Membrane Distillation for Desalination and Other Separations (original) (raw)

Membrane distillation process: Fundamentals, applications, and challenges

IntechOpen eBooks, 2024

Traditional thermal-based processes such as multistage flash and multi-effect distillation have been used for thousands of years to obtain freshwater from saline water. Recently, with the development of membrane-based technology, membrane distillation (MD) as a thermally driven membrane process has received significant attention. The driving force in MD is the vapor pressure gradient induced by temperature difference through hydrophobic microporous membrane pores. The membrane used for MD should be hydrophobic and microporous. In MD, the mechanism of transport involves simultaneously heat and mass transfers, which moves from the hot feed side to the cold permeate side. The performance of MD is evaluated based on various performance metrics including permeate flux, recovery ratio, thermal efficiency, gained output ratio, and specific thermal energy consumption. It has good ability for various industrial uses due to its moderate applied temperature and pressure, high rejection rate, less membrane fouling tendency and its ability to treat high-saline water. The water production cost still remains high compared to conventional processes. Therefore, MD can be cost-effectively when integrated with solar energy, geothermal energy and waste heat. Nevertheless, MD process requires focused research to improve its efficiency to become more mature and economically competitive at large scale.

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.

Membrane Distillation: A cost effective process’

Potential of membrane distillation - a comprehensive review

International Journal of Water, 2013

Membrane distillation (MD) is a recent and unique separation technology, in use in the process industry. The process of separation in MD involves the simultaneous heat and mass transfer through a hydrophobic semi permeable membrane, using thermal energy. Consequently a separation of the feed solution into two components-the permeate or product and the retentate or the return stream occurs. MD utilises low grade or alternative energy, e.g., solar energy, geothermal energy, etc., as a source and is the most cost effective separation technology. Hence the process has come to acquire the attention and interest of researchers, experimentalists and theoreticians all over the world. This article is a comprehensive review of the prominent research in the field of MD technology, including its basic principle, MD configurations, area of applications, membrane characteristics and modules, experimental studies involving the effect of main operating parameters, MD energy and economic, fouling and long-term performance.

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.

Membrane-distillation desalination: status and potential

This paper presents an assessment of membrane distillation (MD) based on the available state of the art and on our preliminary analysis. The process has many desirable properties such as low energy consumption, ability to use low temperature beat, compactness, and perceivably more immunity to fouling than other membrane processes. Within the tested range, the operating parameters of conventional MD configurations have the following effects:(1) the permeate fluxes can significantly be improved by increasing the hot feed temperature (increasing the temperature from 50 to 70°C increases the flux by more than three-fold), and by reducing the vapor/air gap (reducing the vapor air gap thickness from 5 to 1 mm increase the flux 2.3-fold); (2) the mass flow rate of the feed solution has a smaller effect: increasing it three-fold increases the flux by about 1.3-fold; (3) the concentration of the solute has slight effect: increasing the concentration by more than five-fold decreases the flux by just 1.I 5-fold; (4) the cold side conditions have a lower effect (about half) on the flux than the hot side; (5) the coolant mass flow rate has a negligible effect; (6) the coolant temperature has a lower effect than the mass flow rate of the hot solution. Fouling effects, membranes used, energy consumption, system applications and configurations, and very approximate cost estimates are presented. The permeate fluxes obtained by the different researchers seem to disagree by an order of magnitude, and better experimental work is needed.

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.

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 ...

Membrane Distillation for Desalination and Current Advances in MD Membranes

Journal of Applied Membrane Science & Technology, 2023

Desalination is a great technique to address the growing demand for water because it is essential for humans. Water treatment and desalination are two common uses for the membrane-based, non-isothermal MD (Membrane Distillation) process. It works at low pressure and temperature, and heat from waste and solar energy can meet the process's heat requirements. In MD, dissolved salts and nonvolatile contaminants are rejected as the vapors go through the membrane's pores and start condensing at the permeate side. However, because to the lack of a suitable and adaptable membrane, biofouling, wetting and water efficacy are the main problems for MD. Many researchers have recently worked on membrane composites and attempted to create effective, appealing, and unique membranes for membrane distillation. This review article talks about water shortages in the 21st century, the rise of desalination, the use of membrane distillation (MD), recent developments in membrane distillations, developments in pilot scale MD technologies, New developments in membrane fabrication and modification, the desired properties of membranes, and desalination membranes.

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