Dessalement

Résumé

thumb|Usine de dessalement par osmose inverse à Barcelone en Espagne. Le dessalement de l'eau ou désalinisation est un processus qui permet d'obtenir de l'eau douce (potable ou, plus rarement en raison de son coût, utilisable pour l'irrigation) à partir d'une eau saumâtre ou salée (eau de mer notamment). Très généralement, il est plus simple et plus économique de rechercher des sources d'eau douce à traiter (eaux de surface, telles que lac et rivière, ou eau souterraine), que de dessaler l'eau de mer. Cependant, dans de nombreuses régions du monde, les sources d'eau douce sont inexistantes ou deviennent insuffisantes au regard de la croissance démographique ou de la production industrielle. D'autre part, il est souvent rentable de combiner la production d'eau douce avec une autre activité (notamment la production d'énergie, car la vapeur disponible à la sortie des turbines, et perdue dans une usine classique, est réutilisable dans une station de dessalement dite thermique ou fonctio

Source officielle

https://fr.wikipedia.org/wiki/Dessalement

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Design of solar driven supercritical water desalination plant

Grzegorz Adam Koblanski

The objective of this master project is to develop model for the solar driven supercritical desalination plant. Furthermore we propose a possible system integration and examination of its performance in terms of energy and cost effectiveness. The model simulations and calculations are performed using Belsim Vali and in-house LENI developed program OSMOSE. Supercritical salt separation model was created based on the solubility models proposed by Leusbrock and research conducted by Khan and Rogak on salt mixture solubility. This allowed the creation of a salt separation model as a function of pressure and temperature in supercritical conditions. The proposed model is validated in certain range of pure water density and is characterized by 86% water recovery ratio for salts inlet concentration of 4%. During the simulation, a reactor was operated in fixed temperature of 660 K and 221 bar in order to fulfill potable water requirements in terms of TDS value. The simulations results show that through integration of recompression and steam network, a significant improvement in terms of energy usage and cost incurred can be obtain. Steam network integration with double steam step allows to eliminate electricity requirements and increase the exergy efficiency to 3.16%. The majority cost of the system is caused by the investment in the solar system due to linear behavior of costing function for solar installations. It is shown that 75% of overall investment cost is intended for hot utility. However, it was found that profitability can be obtain when secondary products income are taken into account. By possibility of selling industry salts that are separated in the reactor, it is possible to obtain cost of 0.96 CHF per cubic meter of generated potable water. Moreover, to achieve higher economic performance and fresh water recovery ratio hybrid, the “Reverse Osmosis – Supercritical Desalination Plant” system was investigated. It was found that joining two technologies led to significant economic savings together with drastic increase in water recovery ratio up to 91%. This shows that proposed integration not only increased profitability of the installation, but also increased water recovery ratio. Thus showing promising perspectives for possible future desalination systems.

2013

Chargement

Triggered by the Kyoto Protocol and by the aggravation of freshwater scarcity, environmental impacts should soon become key decision criteria for the planning of potable water supply projects, especially when advanced systems such as seawater desalination are at stake. In order to foster the transition of the water industry towards sustainable practices, the present work proposes an integrated design approach dedicated to potable water supply that targets both economic and environmental objectives. At first, the current industrial practices (Chapter I) and the technical characteristics of potable water supply systems (Chapter II) are analyzed via the modeling of the process units used for potable water supply: pumping systems, conventional water treatment processes (e.g. clarification, filtration, disinfection) and advanced water treatment processes (e.g. membrane processes, thermal processes). Using the ISO 14040 standardized Life Cycle Assessment (LCA) method, Chapter III presents the development of a performance indicator that assesses the environmental impacts generated through all stages of the life cycle of potable water supply (i.e. from "cradle to grave"): from the construction of the potable water treatment plant, to its operation and decommissioning. This LCA-based indicator provides a holistic overview of all potential environmental impacts (e.g. green house gases (GHG) emissions, impacts on ecosystems and on human health). It allows to stress out the impact sources and the penalizing steps within potable water supply (Chapter IV): The production of electricity and chemicals required by the potable water treatment plant is highlighted to generate respectively 75% and 15% of the total impacts generated during the life cycle of potable water supply. Different potable water supply scenarios (e.g. potable water supply from ground water, from surface water, seawater desalination, water import from distant water resources) are benchmarked, in order to identify the best solutions as a function of the local context (e.g. type of electricity supply, topographic conditions, feed water quality). Based on the results of the environmental assessment, Chapter V proposes measures for the improvement of the industrial practices of the water sector, targeting energy and chemicals management, electricity sourcing and effluent disposal. Within the same perspective, Chapter VI details an optimization method for the design of the reverse osmosis (RO) membrane process, i.e. the key treatment process for desalination and wastewater reclamation. This method systematically synthesizes RO process configurations and evaluates their performances on economical (total annualized costs), technical (energy requirement, water conversion rate) and environmental criteria (GHG emissions). Evolutionary algorithms are then used to optimize the design of these configurations (process layout and operating conditions) and to identify those featuring the best trade-offs between economical costs and environmental impacts. As case study, the optimization method is applied on a brackish water reverse osmosis (BWRO) desalination project. The characteristics of the optimal BWRO process configurations are calculated as a function of the project constraints (e.g. economical and technical settings, minimum potable water quality), in order to illustrate how this method may support process engineers for the design of desalination plants.

EPFL2008

Chargement

Effects of groundwater on desalinization in coastal reservoir and adjacent aquifer

David Andrew Barry, Jing Xu

Coastal reservoir provides the additional storage capacity of freshwater in coastal zone which greatly alleviate the water shortage in stressed areas, and the salinization of reservoir water degrade the utility of coastal reservoir. Salinization may result from inadequate desalinization in early operation stage, and groundwater as the important source of freshwater to coastal reservoir and adjacent aquifer was obviously have significant impacts on salinization which was in a dearth research. Laboratory experiments and mathematical model were designed to further discuss the influence of groundwater on the desalinization. The results from experiments shown that with the groundwater discharge rate increased, residual saltwater distribution result from intruded fresh groundwater was further moderated. Coastal reservoirs also greatly changed groundwater discharge pathways to sea. Without coastal reservoir, groundwater discharge to sea directly, while with coastal reservoir, part of groundwater would firstly discharge to coastal reservoir, desalinate the reservoir water, and then to sea. Mathematical model was designed for the prediction of the salinity of reservoir water, and the results from model could indicate the accuracy groundwater discharge pathways in coastal reservoir and adjacent aquifer. These results demonstrate the complexity of the groundwater system in adjacent aquifer of coastal reservoir, and may have great implications for future investigations on the predication of water quality during the full operational period.

2019

Chargement

EPFL2008

Design of solar driven supercritical water desalination plant

Grzegorz Adam Koblanski

2013