Multistage Membrane Distillation Research Articles

Air gap membrane distillation unit operated by thermoelectric module

Membrane Distillation (MD) is a promising and evolving technology with substantial potential for efficient freshwater production. However, most of the traditional MD systems typically incorporate several components, including a coolant chamber, coolant stream, coolant pump, chiller, and coolant lines. Eliminating these key components offers numerous benefits to MD systems. Therefore, this work presents an experimental investigation of a novel hybrid air gap membrane distillation (AGMD) unit coupled with thermoelectric modules (TEMs). The thermoelectric module acts as a heat pump by simultaneously providing both the heating and the cooling demands of the air gap membrane distillation unit. In the TEM-AGMD prototype, the hot surface of the TEM is deployed to heat the feed stream to be treated, while the cold side of the TEM is in close contact with the AGMD condensation plate, thereby eliminating the need for the cooling stream, coolant line, coolant pump, chiller, and coolant chamber. Thus, the investigated system exhibited fewer components and needed no pumping power for the cooling stream, resulting in a compact and an energy efficient membrane distillation (MD) system. Results from the experiment indicate that optimal system performance can be achieved by increasing the number of thermoelectric modules, implementing multi-stage membrane distillation, and intensifying the circulating feed flowrate. Furthermore, operating the thermoelectric modules at high power input boosts unit productivity but worsens the unit's specific energy consumption. Moreover, the proposed TEM-AGMD unit can achieve a minimal specific energy consumption of 962 kWh/m3. The proposed prototype boasts an easy design that enables outstanding water desalination with exceptional salt rejection and minimal power consumption. The combination of thermoelectric module with membrane distillation, capitalizing on recent advancements in MD technology, holds great promise for developing a hybrid system for decentralized water treatment and desalination.

Hybrid multi-stage flash (MSF) and membrane distillation (MD) desalination system for energy saving and brine minimization

A hybrid multi-stage flash and multi-stage membrane distillation system for freshwater recovery from the rejected MSF brine is studied. The proposed system reduces environmental impact through reducing the rate of rejected brine, desalination energy and product cost. This is achieved by utilizing the energy rejected from the brine heater to heat a portion of MSF reject that is fed into the MD system since MD systems operate at relatively low temperature and are tolerant to high salinity input. The system includes a multi-stage MD system with a capacity ranging from 75 to 200 m3/day that help in reducing brine volume as model novelty. MD energy is supplied from the condensate leaving MSF brine heater. The effect of MD feed inlet temperature on the performance of stand-alone MD and hybrid MSF-MD systems is investigated for various layouts of the integrated system. Performance of the proposed system is quantified in terms of productivity, MD gained output ratio (GOR), specific electric energy consumption (SEEC), freshwater recovery rate (RR) and water cost. The hybrid MSF-MD system can be used for rejected brine reduction. Parallel feed – parallel coolant integrated arrangement provides the best performance among other configurations, with a productivity, RR, GOR, and SEEC of 218.3 m3/day, 3.544 %, 0.921 and 1.107 kWh/m3, respectively for the MD system. Additionally, the hybrid MSF-MD system yielded about 30,098m3/day, 57.544 %, and 8.583 in productivity, RR and GOR, respectively. MD freshwater cost is reduced by 70 % - 90 % compared to the conventional MD system with an independent energy supply.

Optimization-based technoeconomic comparison of multi-stage membrane distillation configurations for hypersaline produced water desalination

Unconventional oil and gas production raises concerns regarding sustainable management of high salinity wastewaters generated in this process. Membrane distillation (MD) is a thermal desalination process capable of treating hypersaline brines such as produced water. The low single pass recovery in MD systems operated in a single stage requires a large recycle stream to achieve the desired recovery, resulting in high energy consumption and operating cost. Multistage configurations in continuous recirculation operation mode offer the potential to reduce the energy intensity of MD systems. However, rigorous analysis is needed to assess the performance of MD configurations when operating in multi-stage mode. We present an optimization-based comparison of economic and energetic performance for five configurations of MD (including DCMD, AGMD, PGMD, CGMD, and VMD) operating in multi-stage continuous recirculation mode. Our findings demonstrate that multistage operation reduces the treatment cost and energy intensity of all MD configurations compared to single stage MD, with the greatest benefit for VMD and PGMD. AGMD with five stages outperforms other configurations with 3.58 $/m3feed treatment cost, followed by VMD, CGMD, DCMD, and PGMD with 3.8, 4.2, 5.4, and 9.06 $/m3feed treatment costs corresponding to twelve, eight, eight, and sixteen stages, respectively.

Thermoelectric heating and cooling for efficient membrane distillation

This study introduces the concept of thermoelectric desalination which involves deploying an electrically-powered self-contained direct contact membrane distillation (EPSCD) system for efficient desalination. The EPSCD system integrates thermoelectric devices and effectively combines multistage membrane distillation and heat recovery in a single, compact unit to efficiently manage the energy requirement for the desalination process. Inside the EPSCD system, thermoelectric coolers, arranged in parallel electrically, provide the driving force for the process by pumping the heats of condensation (associated with vapor transport) and conduction (through the membrane) from the cold side back to the hot side for vaporization. The proposed system is simple in design and can achieve instant water desalination with excellent salt rejection and relatively low power consumption. Preliminary results indicate that an energy efficiency up to 86% and a corresponding specific energy consumption of 780 kWh/m3 can be achieved with this system.

Synergistic freshwater and electricity production using passive membrane distillation and waste heat recovered from camouflaged photovoltaic modules

A sustainable supply of both freshwater and energy is key for modern societies. In this work, we investigate a synergistic way to address both these issues, producing freshwater while reducing greenhouse gas emissions due to electricity generation. To this, we propose a coupling between a photovoltaic (PV) device and an innovative desalination technique based on passive multi-stage membrane distillation. The passive distillation device is driven by low-temperature heat and does not need any mechanical or electrical devices to operate. The required heat is recovered from the back side of the PV device that, for the first time, mitigates the aesthetic and environmental impact thanks to an innovative surface texture. The aim is to demonstrate the feasibility to generate PV electricity from the sun and, simultaneously, freshwater from the waste heat. The solution is studied by numerical simulations and experiments at the same time, achieving a good accordance between these two approaches. The device is able to produce up to 2 L m−2 h−1 of freshwater under one sun irradiance. Furthermore, a relative photovoltaic efficiency gain of 4.5% is obtained, since the temperature of the PV module is reduced by 9 °C when coupled with the desalination technology. This work paves the way to compact installations made of such passive units, which may easily provide energy and safe water with low environmental and visual impact, especially in off-grid areas and emergency conditions.

Using the sun to co-generate electricity and freshwater

Using the sun to co-generate electricity and freshwater

Solar Seawater Distillation by Flexible and Fully Passive Multistage Membrane Distillation.

Solar-assisted distillation is considered promising to solve the freshwater supply for off-grid communities. In this work, a passive and flexible multistage membrane distillation (F-MSMD) device is devised to produce freshwater via solar distillation with the latent heat of vapor condensation being recycled to enhance its energy efficiency. By designing a siphon effect, source water is continuously wicked into the evaporation layer and the concentrated brine flows out of the device before reaching saturation, which successfully solves the otherwise challenge of salt accumulation inside the device. To achieve such siphon flow, the recycled paper is prepared from spent copy paper and used as the evaporation layer for efficient water delivery owing to its large pore size and high hydrophilicity. An eight-stage F-MSMD device exhibits a stable clean water production rate at 3.61 kg m-2 h-1 in the newly designed siphon-flow mode. This work provides a green route for designing a solar-assisted distillation device.

Optimization of module length and number of stages in a multistage membrane distillation configuration

ABSTRACT Multistage membrane distillation units connected in series for water desalination is considered. The influence of the number of stages and the module length per stage on the overall economics is investigated via simulations using a validated model. Depending on the degree of feed salinity, a suboptimal condition occurs at a structure size of 40 ~ 35 stages with an average module length of 15 ~ 12 m. The corresponding specific operating and fixed costs are $8 ~ 12.5/m3 and $0.97~−.8/m3, respectively. For a high salinity feed, the optimum specific operating cost increases due to reduced mass production. Membrane porosity and thickness showed a pronounced effect on cascade structure economics. The specific operating cost can be further reduced by an average of 60% using permeate heat recovery systems.

Simultaneous production of fresh water and electricity via multistage solar photovoltaic membrane distillation

The energy shortage and clean water scarcity are two key challenges for global sustainable development. Near half of the total global water withdrawals is consumed by power generation plants while water desalination consumes lots of electricity. Here, we demonstrate a photovoltaics-membrane distillation (PV-MD) device that can stably produce clean water (>1.64 kg·m−2·h−1) from seawater while simultaneously having uncompromised electricity generation performance (>11%) under one Sun irradiation. Its high clean water production rate is realized by constructing multi stage membrane distillation (MSMD) device at the backside of the solar cell to recycle the latent heat of water vapor condensation in each distillation stage. This composite device can significantly reduce capital investment costs by sharing the same land and the same mounting system and thus represents a potential possibility to transform an electricity power plant from otherwise a water consumer to a fresh water producer.

Optimization of multistage membrane distillation system for treating shale gas produced water

Thermal membrane distillation (MD) is an emerging technology to desalinate high-salinity wastewaters, including shale gas produced water to reduce the corresponding water footprint of fracturing operations. In this work, we introduce a rigorous optimization model with energy recovery for the synthesis of multistage direct contact membrane distillation (DCMD) system. The mathematical model (implemented in GAMS software) is formulated via generalized disjunctive programming (GDP) and mixed-integer nonlinear programming (MINLP). To maximize the total amount of water recovered, the outflow brine is fixed close to salt saturation conditions (300 g·kg−1 water) approaching zero liquid discharge (ZLD).A sensitivity analysis is performed to evaluate the system's behavior under different uncertainty sources such as the heat source availability and inlet salinity conditions. The results emphasize the applicability of this promising technology, especially with low steam cost or waste heat, and reveal variable costs and system configurations depending on inlet conditions. For a produced water salinity ranging from 150 g·kg−1 water to 250 g·kg−1 water based on Marcellus play, an optimal treating cost are between 11.5 and 4.4 US$ m−3 is obtained when using low-cost steam. This cost can decrease to 2.8 US$ m−3 when waste heat from shale gas operations is used.

Air gap and water gap multistage membrane distillation for water desalination

The performances of multistage air gap membrane distillation (MS-AGMD) and water gap membrane distillation (MS-WGMD) systems are experimentally investigated and compared using three-stages systems for different operating conditions. Parallel, series, and mixed stage-connections are considered. The flux of MS-WGMD is more than double the flux of MS-AGMD. The parallel stages-flow connections produced higher output flux than series connections (15% on average for MS-WGMD and 10% on average for MS-AGMD). The MS-AGMD system is found to be more sensitive to changes in the feed temperature and gap width than the MS-WGMD system. The effect of feed flow rate on permeate flux is higher than the coolant flow rate. The series stage connections are more sensitive to the change in hot and cold flow rates than the parallel connection; particularly the feed flow rate. The productivity of the three-stages system is almost three times the single stage system. The calculated specific electric energy consumption ranged from 5 to 10 kWh/m3 and it values for MS-WGMD system are lower than that of MS-AGMD system, and decreases with increasing the feed temperature.

Multistage vacuum membrane distillation (MSVMD) systems for high salinity applications

Multistage membrane distillation (MD) systems can have significantly higher efficiencies than their single stage counterparts. However, multistage MD system design has received limited attention. In this paper, the performance of a multistage vacuum membrane distillation (MSVMD) which is thermodynamically similar to a multi-stage flash distillation (MSF) is evaluated for desalination, brine concentration, and produced water reclamation applications. A wide range of solution concentrations were accurately modeled by implementing Pitzer's equations for NaCl-solution properties. The viability of MSVMD use for zero liquid discharge (ZLD) applications is investigated, by considering discharge salinities close to NaCl saturation conditions. Energy efficiency (gained output ratio or GOR), second law efficiency, and the specific membrane area were used to quantify the performance of the system. At high salinities, the increased boiling point elevation of the feed stream resulted in lower fluxes, larger heating requirements and lower GOR values. The second law efficiency, however, is higher under these conditions since the least heat for separation increases faster than the system's specific energy consumption with increase in salinity. Under high salinity conditions, the relative significance of irreversible losses is lower. Results indicate that MSVMD systems can be as efficient as a conventional MSF system, while using reasonable membrane areas and for a wide range of feed salinities. Given MD's advantages over MSF such as lower capital requirement and scalability, MSVMD can be an attractive alternative to conventional thermal desalination systems.

Experimental Study on a Multi-stage Air Gap Membrane Distillation (AGMD) Unit

Membrane distillation (MD) is a separation process that involves vapour transport through a hydrophobic membrane. The evaporation is caused by the partial pressure difference between a hot fluid and cold fluid/surface. In this study, an air gap MD (AGMD) process is utilized to produce freshwater from saline solution. A multi-stage AGMD unit with 0.45 mm pore size Polyvinylidene Fluoride (PVDF) membranes is built and experiments have been carried out with different operating variables including feed temperature, coolant temperature, air gap width and feed inlet concentration.A maximum of 12.9 kg/m2 of distillate flux was obtained per kWh energy input from the multi-stage MD unit while for a previously built single-stage MD unit, the highest water/power ratio obtained was only 2.3 kg /m2 kWh. This variation indicates that multistaging is necessary for efficeint energy use in MD system.

Integration Design of Heat Exchanger Networks into Membrane Distillation Systems to Save Energy

Membrane distillation requires a lower operation temperature than other separation processes. It is also able to use low-grade thermal energy. In this study, an integrated design method that utilizes a membrane distillation (MD) system to produce pure water is presented. This method is the integration of the heat exchanger network (HEN) into the MD system, and it uses the waste heat from HEN as the energy source of the MD process so as to greatly reduce the water cost. In this proposed method, a multistage MD system is designed to generate the optimal system structure and operating conditions. Then the output and input MD streams are merged into the existing HEN so that the energy cost of pure water can be determined by redesigning the HEN with the trans-shipment models. The efficiency of the proposed method is demonstrated through an industrial case.

Optimal Design of Multistage Membrane Distillation Systems for Water Purification

In this paper, a novel optimal design strategy is proposed to produce pure water in a multistage membrane distillation (MD) system. It is a systematic approach to modeling and analyzing multistage MD processes. The proposed method can generate the optimal system structure and operation conditions and avoid poor integration and suboptimal configuration of multistage MD systems. In this approach, an innovative module model is first established, and then the cost function relating the capital and the operation cost to the design variables and the structural variables of the designed system is introduced in the objective function. A superstructure flow sheet is presented to describe all the possible flow routes for the cold stream. Then optimal design problem can be formulated as a mixed-integer nonlinear programming (MINLP) problem to minimize the total annualized cost. Based on our simulation studies, the mode of the commonly used countercurrent operation is the optimal flow route for the MD system. The design results would also determine the configuration of the optimal separation stage, the optimal operating mode, and the corresponding operating conditions.

Seawater desalination by an innovative solar-powered membrane distillation system: the MEDESOL project

This paper deals with the MEDESOL (Seawater Desalination by Innovative Solar-Powered Membrane Distillation System) project, partially supported by the European Commission under the Horizontal Programme “Global Change and Ecosystems (Global 4)”. Despite the advantages of solar membrane distillation (MD) systems, very few experimental systems have been developed compared with the mature technologies of solar PV-driven reverse osmosis and solar distillation. The main objective of the MEDESOL project is the development and experimental assessment of the solar multi-stage MD concept in order to develop a high-efficiency and cost-effective system for seawater desalination. EU and developing country scenarios will be analyzed. The layout involves the integration of several membrane distillation modules into a multistage MD system in order to minimize the specific energy consumption. The aim is to develop systems for a capacity range from 0.5 m3/d to 50 m3/d. Technical simplicity, long maintenance-free operation periods and high-quality fresh water output are the most important aims which will enable successful application of the systems that are based on MD. The heat source will proceed from an advanced compound parabolic solar concentrator, developed for the specific concentration ratio to achieve the specific needed range of temperatures, and the seawater heater will include the development of advanced non-fouling surface coatings to avoid scaling. Laboratory tests under defined testing conditions of all components will permit the preparation of successful field tests under real conditions, to be performed in Spain and Mexico.

Zatężanie wodnych roztworów kaprolaktamu metodą destylacji membranowej

The process of concentration of waste aqueous solutions of e-caprolactam (generated during nylon-6 production) by multistage membrane distillation (MD) was described. The own MD experimental set (Fig. 1) has been used. During the MD process the time dependence (up to approximately 50 h) of change of the permeate flux obtained, dependently on the feed concentration expressed as total organic carbon (OWO) content, was determined. The values of electrical conductivity and pH of distillate (Fig. 6 and 7) as well as OWO content in the feed and distillate (Fig. 5) were determined the same time. The high degree of organic compounds' separation was achieved (more than 99.9 %). The distillate obtained was nearly pure water containing barely 220 mg/dm 3 of organic carbon and 60 mg/dm 3 of nitrogen. That distillate was successfully used for polyamide extraction, after its polymerization. The observed in MD process the phenomenon of decrease in membranes' permeability was attributed to membrane pores' wetting as well as to settling of the deposits on the surface (investigations by SEM method, Fig. 2 and 4). It was found that hot water effectively leaches the deposit, consisted of oligomers formed as by-products during e-caprolactam polymerization.

Experiments on seawater desalination by membrane distillation

The membrane distillation process is a new desalination process which offers high quality product water, is simple and highly self-adjusting, and is easy to operate and maintain. However, the results of fundamental experiments with plate-and-frame type modules in a single-stage parallel stack indicate a heat efficiency of less than 50%. To develop a practical membrane distillation process, a multi-stage membrane distillation process and a suitable membrane module with high efficiency needs to be developed to make the heat efficiency of the whole systen as high as possible. In this paper, experimental results on heat efficiency, operating and conditions and product water quality for two kinds of tested molecules are presented.