Flexible Design and Operation of Multi-Stage Flash (MSF) Desalination Process Subject to Variable Fouling and Variable Freshwater Demand

yesThis work describes how the design and operation parameters of the Multi-Stage Flash (MSF) desalination process are optimised when the process is subject to variation in seawater temperature, fouling and freshwater demand throughout the day. A simple polynomial based dynamic seawater temperature and variable freshwater demand correlations are developed based on actual data which are incorporated in the MSF mathematical model using gPROMS models builder 3.0.3. In addition, a fouling model based on stage temperature is considered. The fouling and the effect of noncondensable gases are incorporated into the calculation of overall heat transfer co-efficient for condensers. Finally, an optimisation problem is developed where the total daily operating cost of the MSF process is minimised by optimising the design (no of stages) and the operating (seawater rejected flowrate and brine recycle flowrate) parameters

Energy-water-environment nexus underpinning future desalination sustainability

Energy-water-environment nexus is very important to attain COP21 goal, maintaining environment temperature increase below 2 °C, but unfortunately two third share of CO2 emission has already been used and the remaining will be exhausted by 2050. A number of technological developments in power and desalination sectors improved their efficiencies to save energy and carbon emission but still they are operating at 35% and 10% of their thermodynamic limits. Research in desalination processes contributing to fuel World population for their improved living standard and to reduce specific energy consumption and to protect environment. Recently developed highly efficient nature-inspired membranes (aquaporin & graphene) and trend in thermally driven cycle's hybridization could potentially lower then energy requirement for water purification. This paper presents a state of art review on energy, water and environment interconnection and future energy efficient desalination possibilities to save energy and protect environment

Seawater desalination in micro grids: an integrated planning approach

Background: Islands often depend on the import of fossil fuels for power generation. Due to the combined effect of high oil prices and transportation costs, energy supply systems based on renewable energies are already able to compete successfully with fossil fuel systems for a number of these islands. Depending on local and regional conditions, not only energy supply is a challenge, but also the finding of a reliable supply of water. A promising alternative to freshwater shipments is seawater desalination. Desalination processes can act as a flexible load whenever excess electricity generated by renewable sources is present. Methods: Numerical simulations of combined energy and water supply systems for the Caribbean island Petite Martinique, Grenada, are accomplished. Considering renewable energy sources like wind and solar radiation, energy storage technologies, and desalination processes, various scenarios are introduced and simulated, and the results are compared. Results: An extension of the current energy supply system with renewable energy technologies reduces power generation costs by approximately 40%. The excess energy generated by renewables can supply a significant share of a desalination plant’s energy demand. The levelized costs of electricity and water show that the integration of desalination as a deferrable load is beneficial to the considered micro grid. Conclusions: The implementation of renewable energy generation and desalination as deferrable load is recommendable in Petite Martinique. Possible refinancing strategies depending on the combination of different electricity and water tariffs can be derived and applied to similar business cases in remote regions

Simulation, optimisation and flexible scheduling of MSF desalination process under fouling. Optimal design and operation of MSF desalination process with brine heater and demister fouling, flexible design operation and scheduling under variable demand and seawater temperature using gPROMS.

Among many seawater desalination processes, the multistage flash (MSF) desalination process is a major source of fresh water around the world. The most costly design and operation problem in seawater desalination is due to scale formation and corrosion problems. Fouling factor is one of the many important parameters that affect the operation of MSF processes. This thesis therefore focuses on determining the optimal design and operation strategy of MSF desalinations processes under fouling which will meet variable demand of freshwater. First, a steady state model of MSF is developed based on the basic laws of mass balance, energy balance, and heat transfer equations with supporting correlations for physical properties. gPROMS software is used to develop the model which is validated against the results reported in the literature. The model is then used in further investigations. Based on actual plant data, a simple dynamic fouling factor profile is developed which allows calculation of fouling factor at different time (season of the year). The role of changing brine heater fouling factor with varying seawater temperatures (during the year) on the plant performance and the monthly operating costs for fixed water demand and fixed top brine temperature are then studied. The total monthly operation cost of the process are minimised while the operating parameters such as make up, brine recycle flow rate and steam temperature are optimised. It was found that the seasonal variation in seawater temperature and brine heater fouling factor results in significant variations in the operating parameters and operating costs. The design and operation of the MSF process are optimized in order to meet variable demands of freshwater with changing seawater temperature throughout the day and throughout the year. On the basis of actual data, the neural network (NN) technique has been used to develop a correlation for calculating dynamic freshwater demand/consumption profiles at different times of the day and season. Also, a simple polynomial based dynamic seawater temperature correlation is developed based on actual data. An intermediate storage tank between the plant and the client is considered. The MSF process model developed earlier is coupled with the dynamic model for the storage tank and is incorporated into the optimization framework within gPROMS. Four main seasons are considered in a year and for each season, with variable freshwater demand and seawater temperature, the operating parameters are optimized at discrete time intervals, while minimizing the total daily costs. The intermediate storage tank adds flexible scheduling and maintenance opportunity of individual flash stages and makes it possible to meet variable freshwater demand with varying seawater temperatures without interrupting or fully shutting down the plant at any-time during the day and for any season. Finally, the purity of freshwater coming from MSF desalination plants is very important when the water is used for industrial services such as feed of boiler to produce steam. In this work, for fixed water demand and top brine temperature, the effect of separation efficiency of demister with seasonal variation of seawater temperatures on the final purity of freshwater for both cleaned and fouled demister conditions is studied. It was found that the purity of freshwater is affected by the total number of stages. Also to maintain the purity of freshwater product, comparatively large number of flash stage is required for fouled demister

Optimal scheduling, design, operation and control of reverse osmosis desalination. Prediction of RO membrane performance under different design and operating conditions, synthesis of RO networks using MINLP optimization framework involving fouling, boron removal, variable seawater temperature and variable fresh water demand.

An accurate model for RO process has significant importance in the simulation and optimization proposes. A steady state model of RO process is developed based on solution diffusion theory to describe the permeation through membrane and thin film approach is used to describe the concentration polarization. The model is validated against the operation data reported in the literature. For the sake of clear understanding of the interaction of feed temperature and salinity on the design and operation of RO based desalination systems, simultaneous optimization of design and operation of RO network is investigated based on two-stage RO superstructure via MINLP approach. Different cases with several feed concentrations and seasonal variation of seawater temperature are presented. Also, the possibility of flexible scheduling in terms of the number of membrane modules required in operation in high and low temperature seasons is investigated A simultaneous modelling and optimization method for RO system including boron removal is then presented. A superstructure of the RO network is developed based on double pass RO network (two-stage seawater pass and one-stage brackish water pass). The MINLP problem based on the superstructure is used to find out an optimal RO network which will minimize the total annualized cost while fulfilling a given boron content limit. The effect of pH on boron rejection is investigated at deferent seawater temperatures. The optimal operation policy of RO system is then studied in this work considering variations in freshwater demand and with changing seawater temperature throughout the day. A storage tank is added to the RO layout to provide additional operational flexibility and to ensure the availability of freshwater at all times. Two optimization problems are solved incorporating two seawater temperature profiles, representing summer and winter seasons. The possibility of flexible scheduling of cleaning and maintenance of membrane modules is investigated. Then, the optimal design and operation of RO process is studied in the presence of membrane fouling and including several operational variations such as variable seawater temperature. The cleaning schedule of single stage RO process is formulated as MINLP problem using spiral wound modules. NNs based correlation has been developed based on the actual fouling data which can be used for estimating the permeability decline factors. The correlation based on actual data to predict the annual seawater temperature profile is also incorporated in the model. The proposed optimization procedure identified simultaneously the optimal maintenance schedule of RO network including its design parameters and operating policy. The steady state model of RO process is used to study the sensitivity of different operating and design parameters on the plant performance. A non-linear optimization problem is formulated to minimize specific energy consumption at fixed product flow rate and quality while optimizing the design and operating parameters. Then the MINLP formulation is used to find the optimal designs of RO layout for brackish water desalination. A variable fouling profile along the membrane stages is introduced to see how the network design and operation of the RO system are to be adjusted Finally, a preliminary control strategy for RO process is developed based on PID control algorithm and a first order transfer function (presented in the Appendix).Government gran

AIR PRESSURE ENERGY STORAGE FOR REVERSE OSMOSIS: BENCH-SCALE PROOF OF CONCEPT

Society faces diminishing access to clean drinking water because of increasing global population and the development of modern industries. At the same time, climate change and other environmental problems caused by the increase in fossil fuel consumption the emphasis on reducing dependency on traditional energy resources in the process of potable water production. To address both problems, a small-scale wind powered reverse osmosis (RO) desalination system with a unique energy storage mechanism was envisioned to provide an energy buffer such that fluctuating and intermittent wind can be utilized. Energy is stored in the form of compressed air in a pressure vessel (PV). The feasibility of this innovative design was evaluated for both seawater (35 g/l and 45 g/L NaCl solutions were selected for seawater experiments) and brackish water (15 g/L and 25 g/L NaCl solutions were selected for brackish water experiments) desalination. The RO desalination coupled with the PV energy storage device was tested using bench-scale experiments under different operating conditions. It was found that high initial air pressure can help to produce the greatest flux and good water quality (\u3e98.6% salt rejection), while different crossflow speeds did not affect the performance of energy-buffered experiments. The performance was further tested with simulated fluctuating and intermittent wind speeds to mimic real-world conditions. It was demonstrated that the energy storage tank can largely dampen the variability in applied pressure and discharge rate caused by wind fluctuation and significantly improve the desalination performance for both flux and rejection without any pressure control strategy. Since high quality drinking water (\u3e98.6% salt rejection) was produced under applied pressure as low as 700 psi, the applied pressure could be lowered to reduce energy consumption. Under simulated intermittent wind operation, RO desalination with energy storage showed significant advantage over traditional RO desalination (with no energy storage mechanism) in that PV can store the energy when the wind dies down and the stored energy can be used to produce good quality drinking water when a small amount of energy is available to provide crossflow. The effects of dissolved nitrogen under high pressure on the RO process were also evaluated. The experimental results indicated that comparing with conventional RO, the RO process with PV did not show a consistent benefit or detriment in flux using different feed concentrations from 0 to 45 g/L, but caused a slight improvement on rejection for all feed concentrations

Energía osmótica: modelado, simulación y operación óptima

En la tesis doctoral se pretende lo siguiente: Desarrollar modelos matemáticos para la simulación de procesos de Ósmosis Retardada por Presión (PRO), con énfasis en el gradiente de salinidad, a fin de reproducirlos con mayor precisión. Utilizar los valores reales de las salinidades para determinar la potencia eléctrica alcanzable y evaluar la eficiencia real, teniendo en cuenta las demandas energéticas inherentes al proceso. Proporcionar un análisis de sensibilidad de algunas variables del proceso PRO y predecir los consiguientes cambios en la potencia neta.Estudiar la viabilidad de las desembocaduras estratificadas de ríos, centrándose en la ubicación de las tomas de agua. Evaluar las potencias mediante modelos hidrodinámicos, que describirán las variaciones a lo largo de la desembocadura del río, y buscar un conjunto óptimo de puntos de captación para maximizar la potencia neta. Evaluar la recuperación de energía osmótica a partir de sales de salmueras de desalación, y estudiar posibles configuraciones del proceso, comparando su rendimiento.Departamento de Ingeniería de Sistemas y AutomáticaDoctorado en Ingeniería Industria

Potential and analysis of an osmotic power plant in the Magdalena River using experimental field-data

Producción CientíficaThe Magdalena River mouth in Colombia is studied as a candidate site for a renewable power plant via osmotic energy technology, using pressure retarded osmosis. This power generation plant would operate through the controlled mix of two flows with different salinities (river water and seawater in this case study). A preliminary design of a pressure retarded osmosis power plant is proposed here by means of experimental data acquisition on-site at the river mouth. The obtained net power production is shown to reach 6 MW, with adequate membrane power densities above 5 W/m2. These promising results consider energetic losses involved in the process, which have been further analysed to propose improvement targets in pretreatment processes and membrane permeability.Spanish Ministry of Economy through the project DPI2014-54530-R and the predoctoral grant BES-2015-073871, by the Junta de Castilla y León and European Regional Development Fund, UIC 233, and by the Banco Santander Iberoamérica Research Grants program. Field data acquisition was funded by COLCIENCIAS -Department of Science, Technology and Innovation of Colombia- by the project: 121571451074, resolution 881 – 2015