Adsorption-based Desalination Research Articles

Synergistic ionic liquid encapsulated MIL-101 (Cr) metal-organic frameworks for an innovative adsorption desalination system

The transformations of brackish water into freshwater employing porous materials such as metal-organic frameworks (MOFs) show a great potential for a green environment. But the adsorption-based desalination slows down due to slow water adsorption/desorption rates and inadequate water storage capacity in conventional adsorbents. Therefore, the restructuring of porous MOFs increases water storage and transfer rates. This paper presents a comprehensive investigation on the fabrication of ionic liquid encapsulated MIL-101 (Cr) MOFs (metal-organic frameworks), and its interactions with water for desalination applications. Firstly, the pristine MIL-101 (Cr) is encapsulated with various types/amounts of ionic liquids. Next, these MOFs are characterized via SEM (Scanning electron microscope), FTIR (Fourier transform infrared), XRD (X-ray diffraction), TGA (Thermal gravimetric analysis), N2 adsorption techniques. The water adsorption on these MOFs is performed experimentally for a wide temperature (30–80 °C) and pressure (0 < P/Ps < 0.95) ranges. The effects of the size (or type) as well as the encapsulation ratio of ionic liquids on water adsorption behaviors are conducted. Based on the experimentally proven water adsorption (isotherms and kinetics) data, an AD (adsorption desalination) system is modelled and simulated. Finally, the AD performances in terms of the specific daily water production (SDWP) and performance ratio (PR) are parametrically studied with respect to various regeneration temperature (50–80 °C) and cycle times (100 s–1000 s). It is found that by ionic liquid encapsulation, the water uptakes/offtake rates are expedited up to 48% (for adsorption)/55% (for desorption), respectively. In addition, the water transfer (Δq) improves up to 45% more than the parent MIL-101(Cr) MOFs. Furthermore, the SDWP increases from 38 to 56 m3 of water per tonne of MOFs per day at the regeneration temperature of 70 °C. The simulation results also show that the ionic-liquid-encapsulated MIL-101 (Cr) MOFs generates water (>25 m3 water per tonne of IL-MOFs) at the regeneration temperature of 50 °C and is potential for the next generation desalination applications.

Design of a gravity spin-driven adsorption-based desalination device

Based on the adsorption property of porous materials and the gravitational spin principle, an innovative design of an adsorption desalination device based on gravitational spin-driven phase change materials for heat storage and exotherm was developed. The power required for the conversion of the device compartment is provided by the gravity difference, and the position fixation of the heat insulation baffle is controlled by the magnetic clasp. The source of thermal energy required by the device follows the green and low-carbon principle, relying on sunlight to irradiate the selective coating and convert it into thermal energy, and then transfer the absorbed thermal energy to the phase change material for storage, which increases the solar energy utilization rate by about 80%. The use of phase change materials can maintain the temperature inside the hot chamber at about 70 °C, allowing water molecules to desorb from the silica gel material and water vapor to rise to the top conical roof to condense into fresh water and collect to the mezzanine water storage chamber. The cylindrical chamber is divided into two chambers, hot and cold, and the adsorption and desorption work is carried out simultaneously, with heat loss within 3%. The initial position where the heat insulation baffle is located is equipped with a magnetic buckle, which can precisely control the angle of baffle rotation. The daily water production of a single device is 8.02 kg, and the carbon emission saving is 0.1518 kg. This work is of great significance to the field of energy saving and emission reduction, and the whole can realize self-operation without an electric power drive, which is a novel way of desalination, considering the concept of energy saving and emission reduction and the full utilization of renewable energy.

Research on solar dish/Stirling engine driven adsorption-based desalination system for simultaneous co-generation of electricity and freshwater: Numerical investigation

Poly-production green systems are recently promising alternatives that could produce various useful energy outputs such as electricity, heat, and distilled water with higher efficiencies, lower costs, and eco-friendly benefits. Considering the superior advantages of the dish/Stirling power cycle and adsorption-based distillation system. This study investigates a detailed theoretical dynamic modeling and performance analysis of an adsorption-based distillation system powered by a solar dish/Stirling engine (ADS-SDSE) for combined electricity and freshwater dual-production. Numerical lumped models for the hybrid system components are developed using MATLAB to evaluate the electrical performance and freshwater production of the proposed ADS-SDSE. The models are considered based on opt-geometric approaches, energy balance analyses, and isotherm adsorption simulation to dynamically simulate the ADS-SDSE operation to analyze its performance under real weather conditions in Tianjin, China, for one complete year. The daily, monthly, and yearly performances of the ADS-SDSE are comprehensively evaluated in terms of net electric power, electrical efficiency, specific distilled freshwater productivity, specific cooling power, and the gained output ratio (GOR) of the hybrid system. It is found that the role of the Stirling engine rejected heat recovery remarkably enhanced the inlet feed hot water temperature feeding the adsorptions beds and became uniformly at (82.6−95 °C) throughout the day. Moreover, the proposed ADS-SDSE can produce an electrical power output of about 23.42 kW with solar to electricity efficiency of 23.40%, specific daily freshwater production (SDWP) of about 11.53 m3 per ton of silica gel, 320 W/kg of silica gel specific cooling power, and 0.62 GOR. Conclusively, it can be inferred that the proposed ADS can be powered efficiently by the waste heat of the solar dish/Stirling engine.

Impacts of non-adsorbable gas on the adsorption-based desalination and cooling system with fin branch configurations

Non-adsorbable gas can significantly deteriorate the adsorption dynamics of the adsorption-based desalination and cooling system. In this study, an alternative complete computational fluid dynamic model involving non-adsorbable gas transportation is established. The impacts of non-adsorbable air originating from the incomplete degassing or leakage in the evaporator on the heat and mass transfer characteristics in the adsorbent bed and the performance of the adsorption-based desalination and cooling system are analyzed. Non-adsorbable air can significantly hinder the system performance due to weakened adsorption dynamics and induced additional mass transfer resistance. Moreover, a finned-tube bed attached with branched fins is employed to improve the heat transfer and adsorption dynamics. The impacts of fin configurations on the system performance with non-adsorbable air considered are systematically investigated. Machine learning is employed to construct the quantitative relationship between the fin configuration parameters and the total system throughput. And the optimal fin configuration is further identified via the genetic algorithm. The optimal fin configuration with the fin number of 12 and fin branch angle of 64.4° renders a 24.6% augmentation in the total cooling power and a 20.4% increase in total daily water production, respectively.

Computational fluid dynamic study on the adsorption-based desalination and cooling system

Adsorption desalination (AD) is a potentially competitive alternative for potable water production. Unlike traditional rectangular fins for finned-tube adsorbent bed in the AD system, in this study, bullet- and umbrella-shaped fins are employed in the adsorbent bed to improve the heat and mass transfer characteristics in the adsorption/desorption processes, thus augmenting the system performance. Based on a complete transient mathematical model incorporating a three-dimensional computational fluid dynamic model for adsorber and lumped models for evaporator and condenser, impacts of fin configurations regarding base diameter, tip diameter, and shape factor on system performances considering the adsorbent and the whole bed are comprehensively analyzed. Results reveal that a larger base and tip diameter with a lower shape factor contribute to specific bed productions. The underlining relationship between fin configurations and overall performance (total daily water production, total cooling power, and coefficient of performance) is further explored via machine learning. And the optimal fin shape is identified by the genetic algorithm. The optimal base diameter, tip diameter, and shape factor are 0.262, 0.517, and 4.20, respectively, which render a total water production of 5.20 m3/day with a total cooling power of 0.149 kW and coefficient of performance of 0.855.

Solar powered adsorption desalination system employing CPO-27(Ni)

Adsorption-based desalination system (ADS) is an alternative technology to the traditional water desalination systems as low-temperature sources can operate it. Also, ADSs use environmentally friendly materials, limiting global warming and environmental pollution. This work investigates the performance parameters of ADS powered by an evacuated thermal solar collector theoretically and experimentally. The system uses an advanced sorption material of metal-organic frameworks called CPO-27(Ni). The study estimates optimal operating conditions of ADS under the climate of Egypt. A mathematical model is carried out using MATLAB integrated with TRNSYS software. The study investigates high system performance through two modes; without heat recovery (Mode-1) and heat recovery (Mode-2). The ADS performance is evaluated by specific daily water production (SDWP) and gain output ratio (GOR) parameters. The results show a remarkable superiority for mode-2 as it achieved 10 (m3/ton-day) SDWP and 0.4 GOR, while mode-1 achieved about 5 (m3/ton-day) SDWP and 0.23 GOR at the optimum operating conditions. The improvement ratio using mode-2 reached 88 % of SDWP and 79 % of GOR. Also, the validation results showed a good qualitative and quantitative agreement between the experimental and theoretical data.

Metal foam packed adsorbent bed boosting the performance of the adsorption-based desalination and cooling system

Adsorption-based desalination and cooling system serve as an alternative technology to relieve deteriorated water scarcity and energy shortage. In this study, a complete transient mathematical model considering the complete cycle and the dynamics of all components is developed, where the local mass and heat transfer processes in the adsorption bed are solved via the computational fluid dynamics, whose boundary conditions are obtained via solving zero-dimensional energy and mass balance equations in the evaporator and condenser. Based on the proposed model, bed configuration optimization in a metal foam packed bed regarding metal porosity, bed porosity, and metal and adsorbent type is conducted to augment the system production of cooling and water. Results reveal that the optimal system with a metal porosity of 0.8 and bed porosity of 0.25 exhibits a cooling effect of 8.74 kW and potable water of 300 m3 per day. In addition, the effect of advanced asymmetric cycle condition on system throughput is comprehensively explored. The optimal advanced asymmetric cycle conditions for cooling and water productipn are, respectively, identified, where 11.5% improvement in cooling and 11.3% improvement in water production in water production are achieved.

Advanced adsorption-based osmotic heat engines with heat recovery for low grade heat recovery

Efficiently utilizing the low-grade heat contributes to improving energy consumption structure and energy utilization efficiency, as well as preventing environmental deterioration. To harvest low-grade heat below 80 °C, advanced adsorption-based osmotic heat engines are constructed, which consist of an adsorption-based desalination module for thermally separating the salt solution into concentrated and diluted streams, and a reverse electrodialysis module for converting produced salinity gradient into electricity. Two different heat recovery configurations are employed to improve the heat-to-electricity performance: one is that the cooling power generated in the evaporator is used to cool the condenser and the other is that evaporator is coupled inside the condenser. The transient responses are analyzed and the effects of adsorption/desorption time, switching time, working concentration and heat source temperature on the heat-to-electricity performance are discussed. The efficiency with respect to Carnot efficiency is also presented to provide information on effectively utilized level of the available exergy. Compared with original configuration, the reduced effective condensing temperature in Configuration I and the pressurization effect in Configuration II significantly elevate the working capacity, thus to boost the work extracted. At lower working concentrations and adsorption times, the electric efficiency can be improved via Configuration II, while at higher working concentrations and adsorption times, the advanced configurations hinder the electrical efficiency. In Configuration II, compared with original configuration, the electric power and efficiency are improved by 68.3% and 15.2%, respectively, at a heat source temperature of 333.15 K with 2 mol/kg NaCl solution. While with 7 mol/kg NaCl solution, the electric power is augmented by 11.8% while the electric efficiency is decreased by 19.8%. This study may contribute to designing advanced adsorption-based osmotic heat engines to achieve an upgraded heat-to-electricity performance.

A review of recent advances in adsorption desalination technologies

Adsorption-based desalination (AD) is an emerging concept to co-generate distilled fresh water and cooling applications. The present study is aimed to provide a comprehensive review of the adsorption desalination systems and subsequent hybridization with known conventional cycles such as the multiple-effect AD (MED), solar regenerable, integrated evaporator-condenser cascaded, and ejector integrated systems. The systems are investigated for energy consumption, productivity enhancement, and performance parameters, including production cost, daily water production, and performance coefficient. Comprehensive economic aspects, future challenges, and future progress of the technologies are discussed accordingly to pave researchers' paths for technological innovation. Traditional AD systems can produce specific daily water production of 25 kg per kg of adsorbent. The solar adsorption desalination-cooling (ADC) showed a promising specific cooling power of 112 W/kg along with a COP of 0.45. Furthermore, for a hybrid MEDAD cycle, the gain output ratio (GOR) and performance ratio (PR) is found to be 40%, along with an augmented water production rate from 60% to two folds. The AD technology could manage the high salinity feed water with the production of low salinity water with a reasonable cost of US$0.2/m3.

Field synergy analysis for heat and mass transfer characteristics in adsorption-based desalination and cooling systems

Adsorption-based desalination and cooling system has gained particular interests for low-grade heat harvesting. In this study, field synergy analysis is conducted to illustrate the complicated heat and mass transfer characteristics in an adsorption-based desalination and cooling system with finned-flat beds via a dynamical three-dimensional computational fluid dynamics model. Two field synergy angles α and β reflecting the synergy effect of heat transfer and flow resistance with the adsorption driving force are examined. Results illustrate that smaller α and β result in better adsorption performance. Furthermore, guided by the field synergy analysis, adsorbent bed configurations (fin diameter, fin pitch, fin shape, and fin arrangement) are optimized. The fork-row arrangement results in a higher SCP and SDWP than that of the in-line arrangement. With the fin pitch of 20 mm and fin diameter of 12 mm, the system with fork-row arrangement demonstrates a SCP of 0.363 kW/kg and SDWP of 12.5 m3 per ton silica gel per day, which is 6.6% higher than that of the in-line arrangement as the field synergy parameter between heat transfer and the driving force factor (α) is more predominant at a relatively smaller fin pitch.

Evaluations of adsorbents and salt-methanol solutions for low-grade heat driven osmotic heat engines

To recovery low temperature waste heat, a methanol-based adsorption-driven osmotic heat engine is investigated, which consists of an adsorption-based desalination system for producing concentrated and diluted solutions, and a pressure retarded osmosis system for extracting power from the Gibbs free energy of mixing. Salt-Methanol is used as working solution and the activated carbons and metal-organic frameworks are employed as the adsorbents. Impacts of desorption temperature, salt concentrations, salt types, and adsorbents on the system performance are numerically analyzed. Criteria for screening the adsorbents and salts are evaluated and discussed. Qualified adsorbents should have larger relative pressure where half of the maximum absorption uptake is achieved and moderate adsorption enthalpy. Salt-methanol solutions with larger solubility and osmotic coefficient are beneficial for improving the system energy efficiency. When operating between 60 °C and 20 °C, a maximum energy efficiency of 6.68% was achieved at 5 mol/kg LiBr-methanol solution for MAXSORB3 as the adsorbent with one-stage solid porous matrix regenerator employed. This study contributes to methanol-based adsorption-driven osmotic heat engines for efficient heat to electricity conversion, as well as providing criteria for selecting appropriate adsorbents.

Computational fluid dynamic study on adsorption-based desalination and cooling systems with stepwise porosity distribution

Adsorption desalination (AD) is a promising alternative desalination technology with low energy cost. Conventional studies about AD cycle are mainly based on lumped models that do not involve the details of heat and mass transfer characteristics. In this study, a comprehensive analysis about the effect of stepwise porosity distributions inside a finned-tube bed on system performance is conducted with a transient computational fluid dynamic (CFD) model which captures the bed spatial temperature and pressure distributions, thus to reveal the heat and mass transfer mechanisms. Various bed porosity distribution scenarios at different packed directions are considered. Results reveal that all the forward distributions show an advanced cooling as well as water production. D3-F distribution results in the maximum specific cooling power (SCP) and specific daily water production (SDWP), presenting a 16.2% improvement over that of the uniform at the fin pitch of 55 mm. Moreover, system performances under various operating conditions including ad/desorption time, switch time and heating source temperature are evaluated. The system performance under optimal bed porosity distribution is tested with several adsorbents, among which silica gel of RD type shows a maximum cooling effect of 0.219 kW/kg and water throughput of 7.5 m3/ton-day.

Dynamic modelling and analysis of an adsorption-based power and cooling cogeneration system

In this study, an electricity and cooling power cogeneration system is investigated to harvest low-grade heat below 80 ℃, which consists of a two-bed adsorption-based desalination (AD) system for thermally separating the salt solution into diluted and concentrated solutions while offering cooling power and a reverse electrodialysis (RED) system for converting the Gibbs free energy of mixing of the generated solutions into electricity. The dynamic response of the cogeneration system is presented first, and the asymmetric operation period is analyzed. Then the effects of adsorption/desorptiontime, switching time, working concentration, working fluid mass, and adsorbents on the electric efficiency, coefficient of performance (COP) and exergy efficiency of the cogeneration system are systematically evaluated. Results reveal that longer adsorption/desorption time leads to degraded electrical efficiency and exergy efficiency, and upgraded COP. Extended switching time contributes to COP and exergy efficiency, however, decreases the electric efficiency. Larger salt concentration improves the electric efficiency, however degrades the exergy efficiency and COP. Increasing working solution mass can augment the electrical efficiency, exergy efficiency and COP. Furthermore, refrigeration performance conflicts with power generation performance for different adsorbents. With CAU-10 as the adsorbent, an exergy efficiency of 30.04% is achieved, meanwhile the electric efficiency and COP is 0.39% and 0.84, respectively at adsorption/desorption time of 900 s, switching time of 10 s and working concentration of 8 mol/kg.

Performance evaluations of an adsorption-based power and cooling cogeneration system under different operative conditions and working fluids

In order to harvest low-grade waste heat below 80 °C, we present an alternative adsorption-based power and cooling cogeneration system, which consists of an adsorption-based desalination system for generating concentrated and diluted salt solutions as well as providing cooling power, and a pressure retarded osmosis system for converting the produced salinity gradient energy into electricity. Effects of operation conditions, adsorbents, salt types and solvents are systematically investigated to evaluate the coefficient of performance (COP), electric efficiency, and exergy efficiency of the hybrid system. Results reveal that there exists an optimal desorption temperature leading to the maximum COP and electric efficiency. Larger salt concentration results in upgraded electrical efficiency and exergy efficiency, and degraded COP. Adsorbents with larger relative pressure where the adsorbent achieves half of the maximum absorption uptake and moderate adsorption enthalpy are more appealing. Solvents with high vaporization latent heat and specific heat capacity contribute to COP, however, decrease electrical efficiency and exergy efficiency. Salts rendering a larger osmotic coefficient improve electric and exergy efficiencies, however degrade the COP. When operating at a desorption temperature of 50 °C, the maximum exergy efficiency can reach 33.9%, meanwhile the electric efficiency and COP are 1.63% and 0.87, respectively.

Seawater Desalination Using MOF-Incorporated Cu-Based Alginate Beads without Energy Consumption.

The demand for fresh water is gradually and globally increasing due to the growth of population and water contamination. To meet this global demand, we fabricated metal-organic framework (MOF)-incorporated Cu-based alginate beads (Cu-MOF-Alg beads) for effective removal of water-dissolved salt ions from seawater. Alginic acid formed a matrix for preconfined Cu coordination. In this matrix, the MOFs were successfully in situ synthesized with organic ligands. The as-prepared Cu-MOF-Alg beads exhibited exceptional salt ion adsorption with the extraction of sedimented MOF particles. The adsorption characteristics of the fabricated Cu-MOF-Alg beads exhibited a linear isotherm according to the concentration of Na+ ions. In addition, the beads could be applied over a wide concentration range of target solutions and maintained their ion adsorption capacity after three repeated uses. The beads exhibited rapid adsorption kinetics, and their salt ion removal rate was approximately 94.3% through a multistage adsorption process. The MOF-treated seawater, which was desalinated to a low concentration of 1000 ppm, was filtered by a mangrove-inspired membrane, which yielded a total ion removal rate of 98.1%. Considering the low material cost compared to other adsorption-based desalination techniques and the absence of external energy supply, the proposed hybrid desalination system can produce purified water at an extremely low cost. Thus, this desalination technique could be economically and ecofriendly utilized for practical seawater desalination in a facile manner.

Effect of mass recovery evaporator temperature and condenser temperature on the performance of a solar adsorption-based desalination plant

ABSTRACTWater scarcity increases alarmingly as the population increases. Over the years, a number of salt water desalination techniques have been proposed and reached limitations. The requirement of minimum energy is very well satisfied by an adsorption system, since it can operate with low-grade energy and waste heat exhaust from most industries. The first part of this work discusses the effect of condenser and evaporator temperatures on the performance of silica-gel adsorption cycle mathematically. The second part discusses the performance variations due to mass recovery in the two-bed adsorption system mathematically. It was found that the reduction in condenser temperature and increase in the evaporator temperature both increase the fresh water productivity and cooling capacity of a plant. A desalination plant with mass recovery assistance is superior in performance than the conventional plant. Portable water productivity of 8 m3/day/ton is achieved with the condenser temperature of 15°C and the evaporator temperature of 30°C.

Silica Gel + Water Adsorber Chiller and Desalination System: A Transient Heat Transfer Study

The present work describes a silica gel + water adsorption-based desalination and chiller system, an emerging low cost process of integrating thermal desalination and cooling by utilizing low-grade heat. The cycle employs a combination of flash evaporation and thermal compression of steam in single/two stage to generate the dual effect. The current study aims at simulating a four-bed/stage adsorption system using energy and mass balance along with kinetics of adsorption. The performance of single- and two-stage adsorption systems is compared for ambient temperatures in the range of 25–45 °C and a constant heat source temperature of 85 °C.

Dynamic model for the optimisation of adsorption-based desalination processes

Climate change is leading to an increasing interest in desalination, particularly methods such as adsorption-based desalination (AD), which uses waste heat to co-generate cooling and fresh water from saline water. In this paper, a one-dimensional dynamic mathematical model of an AD system that incorporates transient mass and heat transfer processes in the stream-wise direction of the adsorbent bed is developed, validated and then demonstrated. The model compares well with both adsorbent temperature distributions and water production profiles obtained experimentally by the authors, with small deviations being linked to a number of assumptions including the omission of sorption hysteresis and multi-dimensional transport effects. The validated model indicates that the specific water production rate varies with the cycle time in a complex non-monotonic way, leading to an optimal cycle time for a finite period of operation. The model provides a good basis for optimising AD technology and processes.

Experimental implementation and validation of thermodynamic cycles of adsorption-based desalination

Climate change is leading to an increasing interest in desalination. The large ‘carbon footprint’ of traditional desalination technologies has spurned interest in several potential alternative technologies. This contribution here is concerned with one of these alternatives: adsorption-based desalination (AD), which uses waste heat or solar energy to generate potable water and, depending on the cycle details, cooling as well. We have previously proposed a number of possible theoretical thermodynamic cycles of AD and analysis thereof (Wu et al., Applied Energy 90: 316–22, 2011). In this paper, the practical implementation of these cycles is outlined and their validity experimentally shown. This work means these models can now be used with confidence to better understanding the performance of AD systems.

Low Energy Adsorption Desalination Technology

Adsorption-based desalination (AD) is attracting increasing attention because of its ability to use low-grade thermal energy to co-generate fresh water and cooling. In this paper, the working principle of the AD technology and the possible operation cycles of AD system have been described. A thermodynamic model has been developed in order to study the operational parameters that influence the fresh water production rate (FWPR) and energy consumption of silica gel based AD system. Water adsorption on the silica gel is modelled using a Langmuir isotherm and the factors studied are the heating and cooling water temperatures, which supply and remove heat from the silica gel respectively, and the set temperature of the evaporator. The result shows that the cooling water temperature has far more significant impact on the both water productivity and energy consumption compared to the heating water temperature. The paper also discusses in detail the impact of evaporator temperature on the thermodynamic cycle when the system is operated in desalination mode only.