Air Gap Membrane Distillation Unit Research Articles

Development of membrane distillation powered by engine exhaust for water desalination

To address water shortage in arid areas and make use of waste heat, an experimental investigation is presented for a novel system of air gap membrane distillation unit driven by an engine exhaust heat source for the development of an on-board car water desalination. The design of the gas-to-water heat exchanger is presented and optimized. The system’s performance, governed by the achieved feed water temperature and measured by the output vapor mass flux, is evaluated with time under varying operational parameters, including engine load, engine speed, and feed water flow rate, with the analysis of production cost for economic viability. Experimental results revealed that higher engine loads and speeds lead to rapid temperature increase of the feed water, enhancing the efficiency of the membrane distillation process and increasing the permeate flux. Notably, a maximum permeate flux of 45 kg/m2h was achieved after 40 min of operation. A minimum production cost of 3.2 $/m3 is estimated at an engine load of 35 N.m. With production costs ranging from 3.2 to 5.8 $/m3, the proposed system emerges as a highly competitive option when compared with other membrane distillation systems driven by waste heat in literature. This study underscores the potential of utilizing waste heat from car engines for cost-effective and sustainable water desalination, paving the way for further development and implementation of the system as a mobile desalination unit for different applications.

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.

Biomass-based Brayton-Stirling-AGMD polygeneration for small-scale applications in rural areas

The lack of access to electricity and clean water still affects a substantial proportion of rural areas worldwide, in particular the global south. This paper presents a sustainable polygeneration system that can provide electricity, heat, and drinking water by using agricultural residues in remote rural areas. This polygeneration system consists of a solid biomass-fueled Brayton-Stirling combined cycle system, a boiler, and an air-gap membrane distillation unit. Four different system operation modes were designed to examine the most ideal configurations for maximizing power output, overall efficiency, and/or clean water production, considering a polygeneration system designed for a rural village with daily demands of 13450 kWh electricity and 7.5 m3 drinking water. A thermodynamic analysis are employed to analyze and compare these modes, each operating under steady state conditions. The highest electricity output, up to 160 kW, while the highest clean water is up to 0.7 m3/h. The fuel consumption can reach 0.9 kWh/kg of solid fuel and provide up to 0.0045 m3 of freshwater. In addition, nonlinear multi-objective optimization is used to meet the power demands of typical day in rural areas by varying the polygeneration operation modes and turbine inlet temperature.

Hybridized high concentration photovoltaic unit with enhanced performance air gap membrane distillation unit via depositing reduced graphene oxide layer upon the condensation plate using electrophoretic deposition technique

Amongst the membrane distillation techniques, the air gap configurations showed an outstanding thermal efficiency, while a decline in productivity was recorded due to the additional thermal and mass resistances. The current study proposes minimizing the additional thermal and mass resistances by altering the condensation process to dropwise condensation. Depositing a layer of reduced graphene oxide using the electrophoretic deposition technique on the copper condensation plate was investigated to obtain a hydrophobic nature and attain dropwise condensation. Moreover, different operating conditions were examined for the optimum conditions, which were 45 V, 30 s, 1 cm, and 0.5 mg/ml, for the applied voltage, deposition time, distance between electrodes, and concentration, respectively. This modified condensation plate was investigated experimentally on the lab-scale test rig and showed an improvement in the productivity of 12.5% and 28.5% at the minimum and maximum feed temperatures, respectively. On the other hand, solar energy was utilized to eliminate the heating source required for the membrane distillation unit. A high concentration photovoltaic (HCPV) unit was introduced numerically in the current work with 36 multijunction cells. Furthermore, a microchannel heat sink was successfully designed to keep the cells from thermal degradation. The numerical results showed that the HCPV system could supply hot water up to 55 °C and produce electric power up to 230 W.

Experimental investigation of two novel arrangements of air gap membrane distillation module with heat recovery

Experimental investigations of an air gap membrane distillation (AGMD) unit were carried out to study the energy-saving by heat recovery. The spiral air gap membrane module in the water desalination unit was used. The unit was configured to operate in two novel arrangements and designed to minimize the loss of heat within the drains which maximize the unit productivity as well as the thermal efficiency. Water of salt concentrations 10,000 ppm and 20,000 ppm were used. Measurements of the heat source in the form of inlet and outlet temperatures, water productivity, and thermal efficiency are conducted for different flow rates of coolant and water feeds. The new arrangements are found to save much of the supplied heat, minimize the heat loss, and maximize the unit performance. An enhancement of 38.62% in the water productivity was achieved compared to the conventional AGMD unit. The considered heat recovery system showed water productivity of 155.92 m3/year for the proposed fresh potable water system with a cost of $12.85 per m3.

Membrane Distillation Technology Using for Desalination of Associated Oil Water Production and Study Efficiency of Feed Water Operation Parameter on Air Gap Membrane Distillation Process Production

In this study; membrane distillation technology using to associated oil water production desalination by air gap membrane distillation unit to removed salt from the water after separating oil product, via PTEF commercial hydrophobic membrane distillation with 0.22 µm porous and 0.011 m contact surface area, evaluated the desalination system and operation parameter for feed water effected on process production by employment the distillation under boiling point temperature that getting commercial increments and study the energy gain by calculating the GOR of the desalination process.
 The study focusing on the air gap membrane distillation desalination process by a range of temperature after primary simple sedimentation and filtration it's obtained salt rejection up to 98.9% that proves process separation efficiency. Evaluated the mean operation parameters of feed water affected on permeate water production when selected the feed temperature and flow rate with fixed coolant temperature, coolant flow rate, and air gap width to get an optimum range for feed water operation parameter to obtain optimum value to permeate water production and saving energy.

Experimental Study of a Heat Pump for Simultaneous Cooling and Desalination by Membrane Distillation.

Heat pump systems can simultaneously produce cooling energy for space cooling in hotels, office and residential buildings and heat for desalination using membrane distillation (MD). The MD technique uses a heat input at a temperature compatible with the levels of heat pump condensers (<60 °C). A heat pump prototype coupled with an air-gap membrane distillation unit was constructed and tested. This paper presents the experimental study on a lab-scale prototype and details the two operating modes “continuous” and “controlled” simulating an air conditioning system and a food storage, respectively. The experimental results enable to analyze the performance of the prototype and the physical phenomena involved. Finally, the study shows that this system could be a promising solution to help supplying freshwater to people in hot regions of the world.

Fresh water production by membrane distillation (MD) using marine engine’s waste heat

Ships cruising across the seas have to make sure of ample freshwater supply for the passengers. In this paper, a desalination technique using Multi-Stage Air Gap Membrane Distillation (AGMD) has been proposed to obtain freshwater with the waste heat recovery from a marine engine for on-board ships. The simulation was performed based on the experiments conducted on a lab-scale multi-stage AGMD unit. The seawater to cool marine engine is considered to be the feed solution while the sea surface water is selected as the coolant. The geographical distributions of sea surface salinity and temperature have been considered in the simulation. Effect of the process parameters including the temperature of engine cooling water and sea surface water, air gap thickness, and seawater salinity has been investigated. A transport model has been used to predict the distillate production rate and numbers of MD modules. It is found that this process combined with the ship's engine cooling water could provide a Specific Energy Consumption (SEC) range between 1.58 and 2.63 kWh/m3 for a freshwater demand between 1 to 15 m3/day, considering the pumping energy only. The optimum feed temperature range is found between 65°C and 70 °C for an exit temperature limit of 40 °C.

The effect of ‘High-pH pretreatment’ on RO concentrate minimization in a groundwater desalination facility using batch air gap membrane distillation

This study compared the efficacy of two different scale control strategies: (i) ‘High-pH pretreatment’; and (ii) antiscalant (AS) addition for reverse osmosis (RO) concentrate minimization, in a lab-scale air gap membrane distillation (AGMD) unit. In contrast with previous studies that used a direct contact membrane distillation set-up, we systematically investigated the performance of batch AGMD configuration with and without the preliminary reduction of scale-forming constituents, using high salinity, high alkalinity, high SiO2 and high magnesium hardness RO concentrate. Results indicated that ‘High-pH pretreatment’ by means of the cold lime-soda ash process was more productive than only AS addition to the RO concentrate, resulting in significant salt precipitation when the concentration factor (CF) in the AGMD system increased above 1.3. The High-pH precipitation process provided significant concentration reduction of SiO2 (96%), magnesium (96%) and calcium (86%). Following ‘High-pH pretreatment’, pH re-adjustment and final AS addition, the use of AGMD allowed us to minimize the existing RO concentrate with an initial total dissolved solids (TDS) level of 10.8 g/L by a CF of 3.2. In addition, this chemical demineralization process enabled operation of the AGMD unit at a higher temperature, thus increasing permeate flux.

Modeling and experimental study of air gap membrane distillation unit: application for seawater desalination

Modeling and experimental study of air gap membrane distillation unit: application for seawater desalination

The Performance of an AGMD Unit Coupled with a Water Solar Collector the Experimental Validation for Desalination of Seawater

Our work consists in presenting the results of an invention for a membrane distillation system coupled to an efficient and robust water solar collector which produces potable water with high quality and a small percentage of brackish discharge independent of salinity of the water source. The air gap membrane distillation (AGMD) model for the modules has been developed. This model is based on mathematical equations that describe the heat and mass transfer mechanisms of a single-stage AGMD process. It can simulate AGMD modules in regimes. The theoretical model was validated using in AGMD under different operating conditions and parameters. The predicted water vapor flux was compared to the flux measured at five different feed water temperatures, two different feed water salinities. The model was then used to study and analyze the parameters that have significant effect on scaling-up the AGMD process such as the effect of increasing the membrane length, and feed and coolant flow rates. The model was also used to analyze the maximum thermal efficiency of the AGMD process

Design study of the coupling of an air gap membrane distillation unit to an air conditioner

This work presents the design of a membrane distillation (MD) unit coupled to a refrigeration device. The operation of an MD pilot plant is first tested then simulated using EES solver. The range of hot water feed temperature provided by the condenser of the refrigeration device may vary from 25 to 65°C as needed by the MD unit. The results of the experimental study enable to validate a 1D theoretical model with a maximum deviation of ±6%. This model is combined to a heat pump model to simulate the operation of a coupled machine.The system performance is studied following two scenarios. In Scenario 1 (continuous mode), the system is connected to a seawater network. In Scenario 2 (batch mode), the seawater reservoir is filled up manually every day. The simulation study shows that the increase of the feed water temperature enhances significantly the produced permeate flux but decreases the performance of the heat pump. This system exhibits high exergy efficiency and GOR for a high feed water temperature. Exergy efficiency and gained output ratio (GOR) decrease as the water flow increases and the hot water temperature decreases. Conversely, the coefficient of performance (COP) of the refrigerator increases.

Renewable water: Direct contact membrane distillation coupled with solar ponds

Desalination powered by renewable energy sources is an attractive solution to address the worldwide water-shortage problem without contributing significant to greenhouse gas emissions. A promising system for renewable energy desalination is the utilization of low-temperature direct contact membrane distillation (DCMD) driven by a thermal solar energy system, such as a salt-gradient solar pond (SGSP). This investigation presents the first experimental study of fresh water production in a coupled DCMD/SGSP system. The objectives of this work are to determine the experimental fresh water production rates and the energetic requirements of the different components of the system. From the laboratory results, it was found that the coupled DCMD/SGSP system treats approximately six times the water flow treated by a similar system that consisted of an air–gap membrane distillation unit driven by an SGSP. In terms of the energetic requirements, approximately 70% of the heat extracted from the SGSP was utilized to drive thermal desalination and the rest was lost in different locations of the system. In the membrane module, only half of the useful heat was actually used to transport water across the membrane and the remainder was lost by conduction in the membrane. It was also found that by reducing heat losses throughout the system would yield higher water fluxes, pointing out the need to improve the efficiency throughout the DCMD/SGSP coupled system. Therefore, further investigation of membrane properties, insulation of the system, or optimal design of the solar pond must be addressed in the future.

Experimental investigation of an air gap membrane distillation unit with double-sided cooling channel

Membrane distillation (MD) is a non-isothermal membrane separation process capable of operating at low temperature and low transmembrane hydrostatic pressure. Air gap membrane distillation (AGMD) is one of the MD configurations. In this study, the performance of double-stage AGMD unit at different AGMD-operating parameters such as feed temperature, feed flow rate, coolant temperature, coolant flow rate and air gap width is presented. Experimental results revealed that the built double-stage AGMD unit is capable of achieving a maximum cumulative distillate production of 128.46 kg/m2h, a total (average) flux of 64.23 kg/m2h and a single-stage flux of 65.81 kg/m2h. One key feature of the proposed design is the ability of the unit to use a common cooling chamber to provide the necessary cooling required by the two feed chambers. This reduces the total capital, maintenance and total energy consumption costs. Other benefits include simple module design, easy modules installation and improved system productivity. Furthermore, the system can be operated either as a single-stage or double-stage unit. A simple theoretical model for predicting flux in single-stage AGMD unit was equally presented. The model predicted fluxes with less than 13% discrepancy.

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.

Experimental evaluation and modeling of internal temperatures in an air gap membrane distillation unit

Membrane distillation is a separation process that involves transfer of heat and vapor through a porous hydrophobic membrane. It can be employed for thermal desalination of water by low grade heat obtained, for instance, from low temperature solar collectors. An experimental and theoretical study of an air gap membrane distillation unit is presented. This unit was built from an insulating material to reduce losses, and has a plane parallel geometry. Temperatures are measured at different points in the unit, as well as flow rates and distillate production, to evaluate the different enthalpy flows. In particular, the internal temperatures surrounding the air gap, namely the membrane and cooling plate temperatures, are measured. From these temperatures the diffusion coefficient for vapor in the air gap is evaluated. Experiments are carried out for different values of saline solution temperature and flow rate. A one dimensional heat and mass transfer model with no free parameters is proposed. Temperatures predicted by the model are compared to the experimental results. The correspondence between measured and predicted temperatures is near to 5% accuracy, although the trends of the curves differ somewhat. Possible improvements to the model are discussed.