Membrane-distillation desalination: status and potential (original) (raw)
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Membrane Distillation for Desalination and Other Separations
Recent Patents on Chemical Engineering, 2010
Membrane distillation is an emerging membrane technology used for desalination of seawater or brackish water, solution concentration, recovery of volatile compounds from aqueous solutions and other separation and purification processes. Membrane distillation differs from other membrane technologies in that the driving force for separation is the difference in vapor pressure of volatile compound across the membrane, rather than total pressure. The main advantage of membrane distillation over the conventional thermal distillation is that membrane distillation could occur at a much lower temperature than the conventional thermal distillation. The membranes used in membrane distillation are hydrophobic, which allow water vapor to pass through but not liquid solution. The vapor pressure gradient is created by heating the feed solution and cooling/purging the condensate in the permeate side. Therefore, membrane distillation enables separation to occur below the normal boiling point of the feed solution and could utilize low-grade heat from alternative energy sources. The objective of this review is to cover the basic principles and configurations of membrane distillation process, membrane physical characteristics, heat and mass transfer characteristics, and the effect of operating conditions. Also, major applications of this new technology in desalination, food industry and environmental protection, and latest patent developments and future trend in membrane distillation are presented.
Performance of Membrane Distillation Technologies
The World Scientific Reference of Water Science
Figure 8.1. Principle of MD process utilizing solar and waste heat as two energy sources. making it challenging to compare competing systems, and making fully optimized MD systems rare despite voluminous research. This work aims to clarify and unify the many performance metrics for MD into organized categories. To do so, this chapter divides MD metrics into two primary categories: local and system level metrics. Local metrics include the flux J through the membrane, and the membrane thermal efficiency h th , the latter of which conveys the extent of heat conduction loss vs. evaporation heat transfer. There are also system-level performance metrics, including several ways to express the First-Law Efficiency (e.g., GOR, SEC th), as well as the universal energy efficiency metric, the Second-Law efficiency h II , which depends on entropy generation. A newer system-level metric pair comes from the heat exchanger approach of effectiveness (ε) and number of transfer units (NTU). This chapter aims to explain these metrics by defining each one and conveying what types of performance optimization they are best suited for. Finally, it provides key equations used for converting between different types of metrics, and representative figures that convey how they are interrelated. It adds further detail by examining the performance and key equations for each key MD technology, such as solar-powered desalination. The goal is to concisely provide a framework for best comparing and optimizing membrane materials and MD systems. 8.2. Introduction New technologies continue to grow and emerge to address emerging challenges related to water and energy resources caused by population growth and climate change. 1,2 In water-stressed regions, desalination technologies that extract freshwater from seawater or brackish water are well-established, but efforts continue to make them more efficient and applicable to more water source types.
Experimental Investigation of Membrane Distillation Using Waste Heat for Sea Water Desalination
Engineering Research Journal - Faculty of Engineering (Shoubra)
Membrane distillation is an unprecedented approach demonstrating admirable success in many water purification applications. Recently, many commercial-scale membrane distillation systems with production capacities ranging from 20 L/d to 50 m3/d were improved and assessed. The thermal efficiency and distillate flow of an air-gap membrane distillation (AGMD) system are affected by many factors. We are employing our compact, single-cassette AGMD unit to test these hypotheses. The distillate flow rate of (2,4,6) litter-min could be obtained under the following convenient parameters, cold feed inlet temperature (TC,in) between (25 to 10 oC), hot feed inlet temperature (Th,in) from (40 to 80 oC), feed flow rate (Vf) for both sides from 2 to 6 litter per minutes where distillate flux (Jd) and specific performance ratio (SPR) were considered as the performance indicators for the modelling. To achieve the best results, more than one type of membrane has been used, in addition to utilizing different pore sizes (0.2, 0.45), considering two types of polyvinylidene difluoride (PVDF) thicknesses (100, 200). Apart from this, graphene nanosheets (G) and zeolite nanoparticles (Z) have been added to improve the materials, which will accomplish the best results. All of those experiments are done using local materials obtained from a pilot scale setup located in Egypt.
Thermodynamic design and fouling of membrane distillation systems
arXiv: Applied Physics, 2015
As water shortages intensify globally under the stresses of increasing demand, aquifer depletion, and climate change, the market for efficient desalination technologies has grown rapidly to fill the void. One such developing technology, membrane distillation (MD), has experienced keen academic interest and an increase in start-up businesses in the past decade. MD has expanded into a niche of small scale thermal desalination using solar and waste heat resources, due to its fouling resistance, scalability, and acceptable efficiency. Recent studies indicate that MD could attain the efficiencies of state-of-the-art mature thermal desalination technologies, although additional engineering and scientific challenges must first be overcome. The aim of this research is to better understand and provide solutions for two major challenge areas for MD: efficiency and membrane fouling. Studies on improving MD efficiency included examining the effects of tilt angle on MD performance using numerica...
Membrane Distillation: A cost effective process’
Membrane Distillation (MD) is a thermally-driven separation process, in which only vapour molecules transfer through a microporous hydrophobic membrane. The driving force in the MD process is the vapour pressure difference induced by the temperature difference across the hydrophobic membrane. This process has various applications, such as desalination, wastewater treatment and in the food industry. This review addresses membrane characteristics, membrane-related heat and mass transfer concepts, fouling and the effects of operating condition. State of the art research results in these different areas will be presented and discussed.
Desalination Using Membrane Distillation: A Review
2021
As the water demand increases continuously, large capacities of desalination plant are added every year to meet freshwater demand. The higher carbon footprint of desalinateton raises concern on global climate change. The integration of desalination and renewable energy source could mitigate this water-energy nexus. Due to lack of rain-fall and seawater intrusion, conversion of underground water to salt water is inevitable. Hence, a large capacity of desalination plants has to be installed in various places to convert the saline water in to potable water. Membrane distillation (MD) is a nonisothermal desalination process in which the low-grade heat is used as the driving force. Many researchers have tried to integrate solar energy and MD for sustainable water desalination. Moreover, an alternative source of energy which is from the heat stored in the lower zone of the solar pond was investigated by using the combination of MD and salinity gradient solar pond (SGSP). Solar powered MD ...
Experimental Investigation of High Efficiency Single-Stage Membrane Distillation Configurations
2015
A novel single-stage membrane distillation (MD) configuration, known as conductive gap membrane distillation (CGMD), has been suggested by numerical modeling results to achieve up to two times higher energy efficiencies than conventional air gap MD systems. CGMD consists of an MD module with a high thermal conductivity material in the gap region between the membrane and condensing plate, increasing the effective thermal conductivity of the gap. Such systems, if realized practically, could make MD competitive as a large scale thermal desalination technology that is not restricted only to specialized waste heat applications and could also make a stronger case for MD’s use in waste-heat applications. In this study, an experimental comparison of different MD configurations is carried out on a bench scale system keeping membrane area constant, and results are compared to model predictions. The role of energy recovery within the module on improving CGMD efficiency is illustrated. A system...
Membrane distillation: A comprehensive review
Desalination
Membrane Distillation (MD) is a thermally-driven separation process, in which only vapour molecules transfer through a microporous hydrophobic membrane. The driving force in the MD process is the vapour pressure difference induced by the temperature difference across the hydrophobic membrane. This process has various applications, such as desalination, wastewater treatment and in the food industry. This review addresses membrane characteristics, membrane-related heat and mass transfer concepts, fouling and the effects of operating condition. State of the art research results in these different areas will be presented and discussed.
Desalination, 2002
This work focuses on vacuum membrane distillation (VMD) for seawater desalination. The aim of the work was to compare two hollow fibre module configurations (inside/out and outside/in). Experiments were carried out with pure water and with 15 g/L up to 300 g/L NaCl solutions and for two different material and structure of fibres. Pure water permeability and global heat transfer coefficient were compared for the two configurations. The influence of hydrodynamics on global heat and mass transfer coefficients is discussed.