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For the past several decades, we have seen significant improvements in the desalination industry, mostly intended to increase efficiency and reduce the energy consumption of desalination plants but also to improve the reliability, operability, and longevity of membrane systems. Except for introducing pressure exchanger energy recovery devices, most improvements have been incremental rather than disruptive; in most cases they were small adjustments that made a plant more effective, efficient, or reliable. This paper describes a completely disruptive new method of desalinating seawater: subsea desalination. A patented method combining seawater reverse osmosis (SWRO) membranes with subsea technology is well-proven and has been used extensively in the offshore oil and gas industry for decades. The subsea desalination concept places a membrane desalination plant below sea level, obtaining two very immediate and distinctive benefits: (1) higher and consistent feed water quality and (2) hydrostatic pressure from the column of water that provides all the required pre-membrane pressure. In the paper, we will describe the subsea system design and its advantages, which are substantial and game-changing, explaining how the cost of water can be reduced, reliability improved, and environmental benefits enhanced with such a solution. Specific benefits of the membrane configuration will be discussed, describing the system advantage regarding energy consumption, permeate quality and reduced brine salinity. The paper also presents the set-up and results of subsea field tests where it was proved that the reverse osmosis (RO) membranes performed as predicted by the DuPont WAVE design software. [ABSTRACT FROM AUTHOR]

Abstract: Solar powered desalination has been the focus of great interest recently worldwide. In the past, majority of the experimental investigations focused on solar coupled thermally driven conventional desalination technologies such as Multi-Stage Flash (MSF) and Multi-Effect Distillation (MED). With the advancement in membrane technology and its advantages such as high Recovery Ratios (RR) and low specific energy requirements Reverse Osmosis (RO) desalination has gained popularity. Currently, 52% of the indirect solar desalination plants are RO based with MED and MSF having a 13% and 9% share respectively. Membrane Distillation (MD) based plants represent 16% of the total and have been a focus of recent research efforts. This paper aims to provide a comprehensive review of all the indirect solar desalination technologies along with plant specific technical details. Efforts assessing the economic feasibility and cost affecting parameters for each desalination technology are also reviewed. [Copyright &y& Elsevier]

Abstract: Freshwater scarcity on a worldwide level is now a burning problem, widely discussed in media interviews and in major newspapers. In this context, the majority of the media are underlining the importance of seawater desalination as an attractive and logical alternative source to fight the freshwater scarcity. Unfortunately the majority of all these discussions are providing a totally wrong picture of the real cost of freshwater production from seawater. Figures for desalted water costs from below 0.25 €/m3 to over 0.6 €/m3 for large-scale realisation are frequently quoted. In some media, however, the costs given for desalted water production are too prohibitive for large-scale applications. Many so-called experts are enhancing the confusion with incorrect or in incomplete statements. Even simple considerations, such as water cost ex desalination plant vs. water cost at consumer tap, are neglected. Yet another neglected point is that freshwater of any kind is either highly subsidised or overpriced to finance costs which are not water-related costs. Even in the EU Commission the real cost of seawater desalination is sometimes incorrectly perceived. In principle, the calculation of specific freshwater cost is simple and based on a few clear parameters such as investment cost for a given desalting capacity, energy cost, cost for distribution, amortisation period and concept, financing cost, inflation rate, operation and maintenance cost and, last but not least, plant availability and lifetime. A typical example to illustrate the reigning confusion is the primary energy cost. Today, the barrel of crude oil costs in the world market approximately 70 US$ or more. However, many tenders or BOT projects compare the water and energy cost on a 5 US$/barrel level. With this energy cost level and other unrealistic conditions even oldfashioned, low-GOR MSF plant can produce freshwater for a nominal cost of 0.60 €/m3. With today''s world market prices for crude oil, realistic cost and conditions for financing and all other costs fully covered, the real specific desalted water cost will exceed the 2 €/m3 level for the same plant. It is clear that the freshwater has to be produced at socially acceptable cost and this would be about 1.0 €/m3 or below. However, the calculation of the specific water cost has to be compatible with realistic parameters in order to be able to compare them and to draw correct conclusions and decisions. Therefore, in this paper an attempt has been made to calculate a realistic cost of freshwater from seawater for various types and sizes of desalination plants in combination with various energy sources and with comprehensible realistic conditions utilizing as a basis some older studies. The basic conclusion of our investigation is that large thermal and membrane desalination plants may reach in the future the same level of specific water cost and that a water production cost of 1.00 €/m3, with energy cost of the year 2006 can be achieved with moderate R&D efforts. However, it is difficult (not impossible) to reach 0.50 €/m3 and it will require time-consuming and intensive R&D work to achieve this goal. [Copyright &y& Elsevier]

Abstract: This is the last paper in a series of three parts entitled “Optimal design of hybrid RO/MSF desalination plants”. This research is concerned with exploring the feasibility of hybridization of multi-stage flash (MSF) and reverse osmosis (RO) technologies in order to improve the performance characteristics and process economics ofthe conventional MSF process. The research project involved an optimization study where the water cost perunit product is minimized subject to a number of constraints. In the first part, the design and cost models were presented, the optimization problem formulated and solutions for a number of cases were outlined. In the second part, results were presented and discussed. In this paper we discuss the sensitivity of water cost from the alternative plant designs to variations in some cost elements and operating conditions. In general, it is concluded that, for the same desalting capacity, hybrid RO/MSF plants can produce desalted water at a lower cost than brine recycle MSF plants, while hybrid plants are characterized, by lower specific capital costs and higher water recovery fractions. Reduction in steam cost allows MSF to compete more with hybrid RO/MSF plants. This result explains the advantage of coupling MSF plants and steam power plants where the exhaust steam from the back pressure turbine represents a relatively cheaper source of heat for the MSF process. Results showed that the RO technology exceeds all other designs over the whole range of energy, chemicals and membrane costs studied here. However, water cost of the RO process was the most sensitive to variations in membrane and electricity costs compared to other hybrid configurations. [Copyright &y& Elsevier]

This paper presents the results of an optimization study, based on minimum water cost, to explore the feasibility of the hybridization of RO and MSF processes. The study explores the possible improvement of MSF process economics. Nine different scenarios for the production of the same capacity of desalted water are presented and compared from the standpoint of minimum water cost, specific capital cost and water recovery. The process and cost models, formulation of the optimization problem and solution outlines were previously presented in the first part of this study. In this work, results show that RO technology is recommended when building new desalination plants. RO technology becomes preferable at low feed concentrations and for brackish water desalination. Although they come in second position after the RO process, some hybrid plants economically exceed by far the MSF process. Computations gave a water cost of 1.1 $/m3 for the brine recycle MSF process against 0.75 $/m3 for the two-stage RO process. Water cost of the MSF process can be reduced by 17 to 24% through hybridization with RO technology. [Copyright &y& Elsevier]