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.     

Optimal design of hybrid RO/MSF desalination plants Part II: Results and discussion

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.     

Simulation of M.S.F. desalination plants

A simulation program on the modeling of MSF desalination plants has been developed by the author (ref. 1). The program can be used to accurately either design or simulate plants in actual operation. Proprietory computer programs have been originated by a number of desalination designers for their own use. A few general ones have been published (refs. 2 & 3).The paper describes the design and modeling philosophy utilized in developing the said program. A typical application on Al-Khobar (Phase-I) MSF desalination plant is briefly illustrated as an example for the use of simulation mode of the code.     

考虑水需求的水电联产海水淡化系统的优化设计

水电联产不仅能缓解淡水资源不足的问题,而且可有效降低能耗和淡化成本。建立了水电联产系统数学模型,将优化设计描述为一个混合整数非线性规划(MINLP)问题,并采用混合编码的遗传算法进行求解,结果表明,以水定电模式下水电联产系统最优操作模式为发电、多级闪蒸(MSF)和反渗透(RO)三者的集成,且MSF和RO的产水比存在最优值,发电采用背压式蒸汽轮机。随着淡水需求量的增加,联产系统的淡水成本逐渐降低,MSF与RO的产水比呈现出逐渐降低的趋势。     

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。     

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.     

Desalination in Australia operational experience and future prospects

To provide high quality fresh water to meet peak demands at times of drought in large population centres and to satisfy the requirements for water standards in industrial processes are perhaps the prime attractions of sea water desalination plants. Australia, the driest of earth's continents, will probably have a need for such water supply supplementation and industrial process application long before desalting is applied generally to agriculture or rural production. As the cost of fossil fuel gradually increases, it would also seem likely that the thermal energy required for desalting will come from nuclear fuels. In this paper the existing fresh water resources of the Australian continent are briefly surveyed. Present costs associated with supplying fresh water for industrial and domestic consumption to selected communities at representative locations of the Australian continent are assessed. The technology and economics of large scale sea water desalination plants operating on thermal cycles are discussed. In particular, the multi-stage flash evaporator principle is reviewed and its potential discussed. Consideration is given to the advantages and disadvantages of nuclear powered heat sources. Proposals are made for the control and conjunctive use of reservoirs and desalination plants. The optimisation of desalination plant size and its integration with reservoir storage schemes in two potential Australian locations is discussed.     

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.     

Operation experience with solar powered 10 M3 per day MSF-plant in Kuwait and results of upscaling experiments

This paper reports on the progress which was made in the field of solar desalination in order to obtain reliable equipment capable to both operate under the severe requirements associated with the use of solar energy as a variable source of heat and to yield favourable economic conditions in view of larger scale utilisation of the undepletable source of energy for the generation of fresh water.The results of a 2 year experience with a selfregulating solar MSF desalination plant under the extreme environmental conditions in the middle east will be discussed. A new type of a solar selfregulating fluidized bed MSF desalination unit will be presented for the first time. The new development which has been carried to a mass-production-level is the result of the experience gained in this field over the last years.The operation of the Atlantis desalination unit with different types of solar collection systems, in particular the salt gradient solar pond energy collection and storage system, will be discussed from the technical and economical point of view to demonstrate the feasibility of future larger scale solar desalination.     

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.     

Planning and operational studies in the integrated use of desalination. Case studies for Cyprus and Jersey

Two case studies are described relating to the integrated use of desalination with conventional water resources.The first study describes work undertaken at the request of the Government of Cyprus to advise on the potential role of desalination in the long-term development of the island's water resources. Special features of the study are the strong influence of irrigation demands and the need to devise plans which are flexible against an only partially defined future.The second study relates to the 1.5 mgd MSF plant operated by the Jersey New Water Works Company (Jersey. Channel Islands) where the objective is to maintain overall supply reliability at minimum cost. The plant is operated in conjunction with an unusually complex system of surface water resources which present special difficulties in the optimization of control rules for the desalination plant.     

Analysis of water and power costs by various methods,based on Jeddah IV

The Jeddah IV Power and Desalination Plant is the biggest, dual-purpose plant in the world. Moreover, it is perhaps the first plant of this kind for which authentic cost and operational data are available. As such, it provides a reliable means of assessing the present status of desalination technology and its influence on the cost of power and water.The well-known theoretical methods of cost allocation are used in deriving the product cost from the Jeddah IV plant. The influence of local factors and contractual constraints is discussed. Extrapolations are made to determine the projected cost of water on similar plants but with different performance ratios. Recommendations are made on cost optimization and the most favourable combination for dual-purpose power/desalination plants based on steam turbines and MSF process.     

Optimal design of hybrid RO/MSF desalination plants Part III: Sensitivity analysis

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.     

MSF海水淡化系统热经济学优化分析

热经济学理论和方法在能量系统分析中占有重要地位。本文以年度化平均淡水成本为目标函数,对ＭＳＦ海水淡系统建立了较完善的优化模型。并就国产化日产３０００吨ＭＳＦ海水淡化系统进行了较详细的浮动价格结构下的优化设计分析。     

Multi-objective thermoeconomic optimization of coupling MSF desalination with PWR nuclear power plant through evolutionary algorithms

This paper deals with the application of an evolutionary algorithm to multi-objective thermoeconomic optimization of coupling a multi stage flash desalination (MSF) plant with a pressurized water reactor (PWR) nuclear power plant. The thermodynamic simulation of this initial PWR plant has been performed in a Thermoflex simulator. An Excel add-in called Thermoflex Link has been developed to calculate the exergy of each stream from Thermoflex simulation results. Meanwhile, a computer code has been developed for thermoeconomic and improved combined pinch-exergy analysis in Matlab environment. Both the design configuration (feed water heater structure) and the process variables are optimized simultaneously. The optimization algorithm can choose among several design options included in a superstructure of the feed water heater in dual purpose plant. For the assumptions and simplifications made in this study, a 3000 MW (thermal) PWR power plant such as the Bushehr power plant has been considered. A detailed exergy and exergoeconomic analysis of selected final optimal design identifies the magnitude, location and causes of the thermodynamic inefficiencies. Improved combined pinch and exergy analysis has been applied to display the system information graphically for one to visualize the performance of the system in the initial and final case.     

塔式多效蒸馏海水淡化装置的进料优化

基于全塔负荷均衡的原则，进行了塔式多效蒸馏海水淡化装置的进料优化。结果表明采用优化的三股进料可以使塔内的盐水流量趋于均匀，提高造水比，降低操作的运行费用(电耗和汽耗)，降低预热器的传热面积。而每效的淡化水产量和淡化水累积量几乎不受进料流股数的影响。     

满足不同需求的水热电联产系统的模型和设计简

In order to improve the energy efficiency, reduce the CO2 emission and decrease the cost, a cogenera- tion system for desalination water, heat and power production was studied in this paper. The superstructure of the cogeneration system consisted of a coal-based thermal power plant （TPP）, a multi-stage flash desalination （MSF） module and reverse osmosis desalination （RO） module. For different demands of water, heat and power production, the corresponding optimal production structure was different. After reasonable simplification, the process model ot each unit was built. The economical model, including the unit investment, and operation and maintenance cost, was presented. By solving this non-linear programming （NLP） model, whose objective is to minimize the annual cost, an optimal cogeneration system can be obtained. Compared to separate production systems, the optimal system can reduce 16.1%-21.7% of the total annual cost. showing this design method was effective.     

Nuclear desalination competitiveness in the western region of the Kingdom of Saudi Arabia

The competitiveness of nuclear desalination in the western region of Saudi Arabia was studied. A forecast of water demand between the years 2000 and 2025 was established as part of the input data required for the DEEP computer code. Several options of energy sources such as PWR (600 MWe), SPWR (160 MWth), PHWR (450 MWe), HR (200 MWth) and GT (125 MWe and 175 MWe) were investigated in conjunction with different desalination technologies such as RO, MSF, MED and the hybrid MED-RO. The total plant output, specific electricity investment cost, specific water investment cost, levelized power cost, average daily production, net saleable power and levelized water cost are presented for all cases. Two scenarios were investigated; the first assumed no interest and discount rates and the second assumed interest and discount rates equal to 4%, 8% and 12%. The first scenario assumed that the water utility continues under the control of the government while the second assumed that the water utility will be privatized.     

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.     

A new look at dual purpose, water and power, plants - economy and design features

In light of rapidly rising equipment and fuel costs, recent studies have shown some important results in the economy and optimum designs for dual purpose power/desalting complexes. The desalination cycle chosen for- detailed comparisons in this study is the well known multistage flash (MSF) evaporator, which uses brine recirculation and polyphosphate scale prevention. The multi- stage flash evaporator has found wide spread application in large plants throughout the world. Single units of up to 1400 m3/hr (9.5 MGD), acid dosing, have been built and are now in operation. In general due to corrosion problems, polyphosphate plants are now preferred over the acid one.

A number of schemes for the combined production of power and. water were chosen, mainly a combination of MSF Unit with each of the following power cycle:

• 1- Automatic extraction steam turbine

• 2- Simple gas turbine with waste heat boiler

• 3- Back pressure steam turbineThis paper presents a study of the economic aspects, thermodynamic features and optimization analysis of each of these combined power and water production plants.

The optimum value of the performance ratio and its effect on reducing the cost of water in each of the above mentioned schemes would be discussed in this paper.