Entropy generation in multi-stage flash desalination plants

The present study is applied on the seawater multi-stage flash (MSF) desalination plant that is currently under operation in E-Zuetina operations plant located in Libya. The plant contains 21 evaporator stages at capacity of 10025 (ton/day). The presented operating data has been collected during a visit of the plant, a mathematical model for multistage flash (MSF) desalination plants was developed. The model was based on basic principles of physics and chemistry that describe the stages occurring in the desalination process. The input plant parameters that are known to affect the operation of the MSF desalination plant and its performance were taken into account in the construction of the model. These parameters included make-up flow, brine recycle flow, seawater flow, seawater temperature, seawater concentration, steam temperature and the plant load. For each stage, the developed model was used for predicting the temperatures and pressure of the brine, distillate, cooling brine, and the flow rates of brine outlet and distillate production. The developed model was evaluated with the MSF plant vendor simulation results and its actual operating data. The evaluation indicated that model predictions matched well with the vendor simulation results and the plant operating data. The developed model is sufficiently accurate and model predictions can be relied upon. Therefore, it may be recommended for determining optimum set point of a running MSF desalination plant at different loads to maximize the water production or minimize energy consumption. It can also be used to calculate controller set points for different loads of the plant. Keywords:E-Zuetina MSF Desalination Plant, case study, stage model, brine heater.

The chemically aggressive environment generated in some parts of equipment at multi-stage flash (MSF) desalination plants can cause corrosion problems. The proper selection of materials with higher resistance to corrosion is considered as one of the most prospective approaches for smooth and efficient running of the plants. Because of this, the study of the corrosion behavior of selected materials is an important issue in the realm of desalination technology. This paper reviews the performance of materials used in different MSF desalination plants. The corrosion behavior of materials in different sections of plants, under surrounding environmental conditions, is discussed. Various types or forms of corrosion occurring in different units of plant are described and the strong role of local attack is emphasized. Case histories dealing with failure of components in different plants are cited. The criteria for the selection of materials, which depend upon the nature of environment and operating conditions, are exemplified. The merits and demerits of materials currently employed are highlighted and introduction of new materials either in existing plants as the possible replacements or in future plants are discussed.

Multi stage flash desalination plant with brine–feed mixing and cooling

In this paper, a mathematical model for multistage flash (MSF) desalination plants was developed. The model was based on basic principles of physics and chemistry that describe the stages occurring in the desalination process. The input plant parameters that are known to affect the operation of the MSF desalination plant and its performance was taken into account in the construction of the model. These parameters included make-up flow, brine recycle flow, seawater flow, seawater temperature, seawater concentration, top brine temperature (TBT), steam temperature and the plant load. For each stage, the developed model was used for predicting the temperatures of the brine, distillate and cooling brine, and the flow rates of brine outlet and distillate production. The developed model was evaluated with the MSF plant vendor simulation results and its actual operating data. The evaluation indicated that model predictions matched well with the vendor simulation results and the plant operating data. The developed model is sufficiently accurate and model predictions can be relied upon. Therefore, it may be recommended for determining optimum set point of a running MSF desalination plant at different loads to maximize the water production or minimize energy consumption. It can also be used to calculate controller set points for different loads of the plant. Copyright © 2011 John Wiley & Sons, Ltd.

This paper presents a methodology and practical guidelines for developing predictive models for large-scale commercial water desalination plants by (1) a data-based approach using neural networks based on the backpropagation algorithm and (2) a model-based approach using process simulation with advanced software tools ASPEN PLUS and SPEEDUP and compares the relative merits of the two approaches. This study utilizes actual operating data from two of the largest multistage flash (MSF) and reverse osmosis (RO) desalination plants in the world. Our resulting neural network and process simulation models are capable of accurately predicting the actual operating data from commercial MSF desalination plants, but the accuracy of a neural network model depends on both the proper selection of input variables and the broad range of data with which the network is trained. A neural network model can handle noisy data more effectively than statistical regression and performs better in predicting the performance variables of both MSF and RO desalination plants. Our neural network model compares favorably with recent neural network models developed by others in accurately predicting actual operating data from commercial MSF desalination plants. When compared to a data-based neural network, a properly validated model-based process simulation (as in the case of MSF desalination plants) can more effectively quantify the effects of varying operating variables on the desalination performance variables. When it is difficult to develop a model-based process simulation (as in the case of RO desalination plants), we can use a data-based neural network to accurately predict the desalination performance variables.

This article presents the results of an investigation on the corrosion of flash chamber floor plates in a multistage flash (MSF) desalination plant. In an MSF plant, desalinated water is produced by flashing deaerated seawater in successive flash chambers under reduced pressure. The flash chamber floor plates were made of carbon steel with AISI type 317L stainless steel (UNS S31703) internal cladding. The thickness of the carbon steel and cladding was 8.5 and 3 mm, respectively. Approximately four years after the plant was commissioned, indications of corrosion processes, in the form of numerous red-colored spots, were noticed on the floor plates.

Highly efficient corrosion inhibitor for C1020 carbon steel during acid cleaning in multistage flash (MSF) desalination plant

Neural networks for the identification of MSF desalination plants

Thermal desalination technologies are very energy intensive. The utilisation of nuclear energy for seawater desalination provides a safe, feasible and economic solution for the production of very good quality water. The Multi-Stage Flash (MSF) desalination plant of the Nuclear Desalination Demonstration Project (NDDP) of the Department of Atomic Energy (DAE), Government of India, is coupled with a nuclear power plant on the south east coast of India to share the common facilities and steam. The MSF desalination plant is under construction. This paper describes a case study of the coupling aspects of the MSF desalination plant with the existing nuclear power plant and gives an estimate of the loss of electrical power generation due to extraction of steam. Loss of electrical power is also compared with the Desalination Economic Evaluation Program (DEEP) of the IAEA.

Second-law analysis (SLA) is an important concept in thermodynamics, which basically assesses energy by its value in terms of its convertibility from one form to another.[...]

Fault diagnosis for an MSF desalination plant by using Bayesian networks

This study outlines the estimation of entropy generation of a stored liquid-vapour combination. A salient feature of the present study is the incorporation of a separated flow model for the calculation of entropy generated by a diabatic two phase system. Equations of state corresponding to different thermodynamic equilibria are used for these calculations. Two distinct expressions are proposed for the determination of the total entropy generated by the diabatic saturated two phase system that comprise liquid and ullage regions. The dissipative energy losses in various liquid-ullage systems is quantified through the derived mathematical relations obtained for the overall entropy generated by the system. These developed expressions form the basis of an experimental determination of the entropy generation rate. A parametric study on temperature influencing entropy generation has been performed in the context of different thermal transport mechanisms. The influence of fill levels on entropy generation was also analysed by considering a low and an intermediate filling ratio. The study concluded the influence of central zone of thermodynamic equilibrium with maximum wall convection and minimum concentration gradient on the overall entropy generated by the system. References A. Bejan. A study of entropy generation in fundamental convective heat transfers. ASME J Heat Transfer, 101, 1979, 718--725. doi:10.1115/1.3451063 A. Bejan. Second law analysis in heat transfer. Energy, 5, 1980, 721--732. doi:10.1016/0360-5442(80)90091-2 S. Sarangi. and K. Chowdhury. On the generation of entropy in a counter flow heat exchanger. Cryogenics, 22, 1982, 63--65. doi:10.1016/0011-2275(82)90095-9 P. K. Nag and P. Mukherjee. Thermodynamic optimization of convective heat transfer through a duct with constant wall temperature. Int J. Heat and Mass Transfer, 30, 1987, 401--405. doi:10.1016/0017-9310(87)90128-1 A. Bejan A thermodynamic optimization of geometry in engineering flow systems. Exergy Int. Journal, 4, 2001, 269--277. doi:10.1016/S1164-0235(01)00028-0 V. D. Zimparov Extended performance evaluation criteria for enhanced heat transfer surfaces: heat transfer through ducts with constant heat flux. Int J. Heat and Mass Transfer, 44, 2001, 169--180. doi:10.1016/S0017-9310(00)00074-0 H. Abbassi Entropy generation analysis in a uniformly heated micro channel heat sink. Energy, 32, 2007, 1932--1947. doi:10.1016/j.energy.2007.02.007 F. J. Collado The law of stable equilibrium and the entropy-based boiling curve for flow boiling. Energy, 30, 2005, 807--819. doi:10.1016/j.energy.2004.04.007 J. V. C. Vargas and A. Bejan Thermodynamic optimization of the match between two streams with phase change. Energy, 25, 2000, 15--33. doi:10.1016/S0360-5442(99)00052-3 P. K. Nag Engineering Thermodynamics. Tata McGraw-Hill Publishing Company Limited, 2nd Edition, 1996. W. M. Rohsenow, J. P. Hartnett, Y. I. Cho, Hand book of Heat Transfer. McGraw-Hill New York,3rd Edition, 1988. D. Rakshit, R. Narayanaswamy, T. Truong, K. P. Thiagarajan An experimental study on the interface mass transfer governing thermodynamics of stored liquids. Proceedings of the 20th National and 9th International ISHMT-ASME Heat and Mass Transfer Conference, January 4--6, 2010, Mumbai India. C. Balaji, M. Hˆlling, H. Herwig Entropy generation minimization in turbulent mixed convection flows. International Communications in Heat and Mass Transfer, 34, 2007, 544--552. doi:10.1016/j.icheatmasstransfer.2007.01.015 F. P. Incropera, D. P. Dewitt, T. L. Bergmen, A. S. Lavine Introduction to Heat Transfer. John Willey and Sons, 5th Edition, 2005. P.E. Liley, Steam Tables in SI Units, private communication. School of Mechanical Engineering, Purdue University, West Lafayette, IN., 1984. V. V. Malyshev and E. P. Zlobin Evaporation of liquid hydrocarbons in heated closed containers. Translated from Inzheneruo-Fizicheskii Zhurnal, 23, 4, 1972, 701--708. doi:10.1007/BF00835847

Over the past few decades, the growth of the earth’s population has increasingly contributed to global warming, and increased demand for fresh water on top of a need for a greater power supply. This paper will analyze the integration of a combined- gas turbine with intercooler and a multi-stage flash (MSF) desalination plant for the simultaneous generation of electricity and supply of water and improved performance. The paper will also examine the calculation of the production cost and the capital cost of the MSF desalination plant. The thermo-economic analysis of the study was conducted using the IPSEpro software system. Also, exergy losses of the gas turbine and MSF desalination unit were also calculated. The desalination plant uses the exhaust gases from the gas turbine, as a form of thermal energy, and discharges to feed the seawater heater. A portion of the desalinated water is used to cool the compressed air in the intercooler heat exchanger. Results indicate the improvement in the gas turbine’s performance when desalinated water is used for the intercooler between compressor stages, as the power output increased by 59% over the the simple gas cycle and found decrease with an increase in the ambient temperature. The desalinated water cost was calculated to be $1.7 per cubic meter after determining the optimal configuration and operating conditions. A decrease in steam cost by 36% was observed when the waste heat from the gas turbine was used as the source of thermal energy. Part of this reduction can be explained by the observation that the desalination plant’s pumps consume part of the power generated by the gas turbine.

Over the past decade, the author, Roger Francis, has looked at some very expensive corrosion failures in desalination plants. Avoiding Corrosion in Desalination Plants tells the reader how to avoid existing corrosion problems and how to avoid them in new builds. This book looks at corrosion problems specific to MSF, MED, and SWRO desalination plants, describing their causes, some solutions, and the relative performance of various materials. It gives advice on procuring materials for desalination plants to avoid quality problems. The world’s population is steadily increasing and with it is an increasing demand for water—for both drinking and irrigation. In many areas of the world, particularly in warmer climates, there are limited sources from rivers and wells, so desalination is being increasingly used to produce water to satisfy both requirements. Although desalination is sometimes carried out on brackish waters and highly saline well waters, most desalination plants generate fresh water from seawater. There are three main processes used in desalination plants, the oldest of which is multistage flash (MSF), where the water is essentially boiled at low pressure and the steam that flashes off is condensed for drinking water. The second process is multiple-effect distillation (MED), in which low-pressure steam is used to force evaporation of seawater and the vapor is then condensed for drinking water. Although actual MSF and MED plants (large-scale) are land based, small-scale units have been fitted to large ships, such as cruise liners, to generate fresh water. The third process is seawater reverse osmosis (SWRO), where chloride is selectively removed from water by forcing it at high pressure through a special membrane. This method involves no heat transfer but requires enough electricity to power the high-pressure pumps that are required. All three of these methods have advantages and disadvantages. This book looks at corrosion problems specific to MSF, MED, and SWRO desalination plants, describing their causes, some solutions, and the relative performance of various materials. It gives advice on procuring materials for desalination plants to avoid quality problems.

Novel multi-stage flash (MSF) desalination plant driven by parabolic trough collectors and a solar pond: A simulation study in UAE