Freeze Desalination Research Articles

Performance analysis of coupling vapor compression cycle to freeze and humidification-dehumidification based high-performance desalination

Although freeze desalination has a lower latent heat of ice formation (334 kJ/kg), its energy performance is still insufficient because of energy loss associated with not using the waste heat of the active cooling system. To address this challenge, this research introduces an innovative hybrid desalination system that synergistically combines freeze, humidification-dehumidification (HDH), and vapor compression cycle (VCC) technologies. The novelty of our approach lies in simultaneously leveraging the VCC's cooling and thermal energy for freeze and dehumidification processes, respectively, which greatly increases the desalination energy performance over only achieving freeze desalination. A thermodynamic model is developed to analyze the proposed system, and a series of parametric analyses are carried out to determine the system configuration that obtains the highest performance. Ultimately, a higher ice recovery rate of 20 % offers the best total desalination performance of only 63 Wh/kg. Furthermore, the HDH desalination unit can make up the for loss of freeze desalination performance at higher feed seawater temperatures, ensuring robust performance even under high-temperature conditions.

A model of freeze desalination for predicting salt concentration in ice using the laws of conservation of matter & mass

The assessment of freeze desalination (FD) efficiency is lagging behind due to the lack of an effective means of determining ice total dissolved solid (TDS). In this paper, an ice TDS prediction model was constructed by utilizing the law of conservation of matter (LCMat) and conservation of mass (LCMas) in the icing process. It was concluded that the average TDS ice crystals in any icing process was correlated with the TDS of the raw (concentrated) water at the starting of freezing, the salt mass change rate of the concentrate water, and the volume of ice crystals. A one-way FD test was carried out using the saltwater from South Xinjiang, and the exponential equation model and linear equation model of LCMat-LCMas were derived, and the simulation accuracy of LCMat-LCMas was verified by using the test data. The results show that the model has high prediction accuracy. The exponential equation model is suitable for predicting the ice TDS for ice with thickness within 15 cm, and the linear equation is suitable for predicting the ice crystal TDS for ice thicker than 15 cm. Further validation of the model accuracy is needed for larger cooled areas and icing thicknesses, and multidirectional icing processes.

Review on advanced techniques in zero liquid discharge water desalination via humidification-dehumidification within thermally-driven transport reactors

The article examines an advanced zero liquid discharge (ZLD) desalination method focusing on humidification-dehumidification (HDH) in thermally driven transport reactors. The limited availability of water, particularly in dry locations, has prompted the advancement of several desalination techniques. Reverse Osmosis (RO) is a prevalent membrane technology in the market; however, it has restrictions regarding brine disposal. ZLD technologies strive to mitigate environmental consequences by transforming saltwater into drinkable water and precious salts while minimizing waste. Membrane Distillation and Crystallization (MD-C) is notable as a highly efficient Zero Liquid Discharge (ZLD) technique. Despite its high energy consumption, it can combine MD-C with renewable or waste energy sources to improve sustainability. Freeze Desalination (FD) was reviewed for its economic efficiency, especially when utilizing cold energy from liquefied natural gas (LNG). Hybrid systems that combine Forward Osmosis (FO) and membrane distillation with condensation (MD-C) can potentially improve water recovery and decrease energy usage. The HDH desalination process imitates the natural precipitation process, examines its ability to operate at low temperatures, and highlights its potential for integration with renewable energy sources. The review discusses the HDH design, the effect of salinity on its performance, and the different dehumidification technologies. It emphasizes the significance of creative methods in achieving sustainable water management.

Comparing energy and exergy of multiple effect freeze desalination to MEE MSF RO

Freeze desalination is a promising technique for wastewater treatment and zero/minimum liquid discharge systems, often requiring multiple stages to produce potable water. This research focuses on developing a Multiple Effect Freeze Desalination (MEFD) system based on experimental data for Single-Stage Desalination Efficiency (SSDE) and Single-Stage Recovery Rate (SSRR). The study analyzes various MEFD setups, calculating cooling energy consumption and correlating it with electrical usage through the coefficient of performance (COP). Comparisons with Reverse Osmosis (RO), Multi Effect Evaporation (MEE), and Multi-Stage Flashing (MSF) suggest that MEFDs may face challenges in matching RO efficiency but can compete with MEE and MSF within specific operational ranges. Exergy assessments indicate difficulties against even 10-stage MSF systems. Achieving SSDE and SSRR levels above 65% enables MEFDs to rival 10-stage MSF plants in terms of energy efficiency, surpassing MEE and MSF at over 85% efficiency. Despite these challenges, MEFDs offer benefits for treating high salt concentrations and resisting corrosion.

Study on freezing separation process through observing microstructure of NaCl solution ice

Freezing desalination is a method to purify saline water. Researchers believe that the salt inclusions distributed inside ice affect the sea ice salinity, but there is not sufficient visualized proof that has been obtained via direct and non-destructive experiments to support this view. Even less study has been carried out on the salt inclusion distribution inside ice below the eutectic temperature. In this paper, a NaCl solution ice sample was prepared with the original mass concentration of 3 wt% using unidirectional heat transfer method. The freezing temperature was −24 ℃, which is lower than −21.2 ℃, the eutectic temperature of NaCl solution. Micro-CT device was used to scan the upper, middle and lower parts of a 3 wt% NaCl solution ice sample and the 5-layer U-Net architecture in DL (deep learning) module of the Dragonfly program was used to segment images to extract the information of interest. The image characteristics of salt inclusions and air bubbles inside the ice were obtained. Very high salt inclusion area proportion was found in the surface layer images of the sample with the maximum area proportion of about 43%. Experiments were also carried out to measure the salinity distribution inside the same solution ice samples. It was found that in the surface and bottom ice layers, the salinity is higher than that of the original solution. In the experiments, for the layers cut from the top and bottom of the 3 wt% NaCl solution ice sample, each of them possesses 10% of the solution ice sample mass, their salinities were 4.28 wt% and 5.41 wt%, respectively. Comparing the measurement results with the micro-CT image processing results, it was found that the variation tendency of the area proportion of salt inclusions is consistent with that of the ice layer salinity. The combination of micro-CT technology with DL image processing method has been proved an effective way to visualize and analyze quantitatively the internal structure of salt solution ice. Then, three NaCl solution samples that have the original mass concentrations of 3 wt%, 6 wt% and 9 wt%, and a pure water sample were frozen under the same conditions. The middle parts of the four ice samples were scanned and the obtained micro-CT images were processed. It can be found that in the middle parts of the three NaCl solution ice samples, the area proportions of salt inclusions increase from top to bottom and are positively correlated with the original salinities of the solution ice. The factors affecting air bubble distribution are more complex than that affecting salt inclusion distribution.

Effects of salinity and temperature on the icing of sessile saltwater droplets on solid surfaces

The icing of sessile seawater droplets on solid surfaces holds significant importance in scientific research and freeze desalination technology. Nevertheless, the statistical characteristics and underlying mechanisms of this phenomenon remain insufficiently understood. In this study, we experimentally investigate the statistical characteristics of the icing of seawater droplets on solid surfaces, and couple with the molecular dynamics method to reveal the influence of salinity and substrate temperature on the icing. It is found that the nucleation time of seawater droplets on solid surfaces exhibits stochasticity, while it follows a normal distribution. With increasing salinity or surface temperature, the distribution range of the nucleation time becomes broader and more dispersed. Both the average nucleation time and the average freezing time of seawater droplets increase with increasing salinity or temperature; the former is due to an elevating nucleation energy barrier, and the latter stems from an increasing ice-salt solution interfacial free energy (the energy required to freeze the salt solution into a unit area of ice). Our findings enhance the comprehension of the characteristics and fundamental mechanisms of the icing of seawater droplets on solid surfaces, offering valuable insights for the development of freeze desalination technology.

Electric Field-Enhanced Ion Rejection Rate in Freeze Desalination.

Freeze desalination is an appealing method for seawater desalination through freezing seawater. The percentage of ions in the liquid phase, which is termed ion rejection rate, is a critical factor affecting the performance of freeze desalination. Improving the ion rejection rate is an important topic for freeze desalination. In this work, we investigate the effects of electric fields on the ion rejection rate during the freezing of seawater through molecular dynamics simulations. It is found that the ion rejection rate increases with increasing electric field strength. The enhanced ion rejection rate is due to the reduction of the energy barrier at the ice-water interface caused by the electric field, which affects the orientation of water molecules and ion-water interactions. However, the electric field hinders the ice growth rate, which affects the productivity of freeze desalination. Nevertheless, the finding in this work offers a new idea to improve the ion rejection rate. Practically, a trade-off needs to be found to optimize the overall performance of freeze desalination.

Experimental analysis of freezing desalination using gravity and centrifugal methods with economic evaluation of coupled freezing desalination and ice storage system

This study conducted experiments to compare the desalination efficiency of gravity and centrifugal desalination methods for freezing desalination, showing the superiority of centrifugal desalination. Moreover, through experiments on supercooled water production, it was determined that supercooled water can operate stably at an evaporator temperature of −4.5 °C, and its supercooling state can be released using ultrasound. Based on the experimental results, a novel system that combines freezing desalination with ice storage is proposed. The proposed system utilizes supercooled water for ice production and centrifugal post-treatment, using desalinated ice as a cold storage medium to integrate desalination and ice storage. The proposed system showed a 30 % lower total capital cost compared to conventional systems, with a payback period of 38.18 % lower than conventional system (5.42 years). Additionally, the system demonstrated optimal economic performance when utilizing 80 % of its ice storage capacity, with a payback period of 3.38 years, contrasting with 7.62 years when utilizing 20 % storage capacity. The application of this system in four regions with varying peak and off-peak electricity prices, including Guangdong, Fujian, Hainan, and, France revealed that the system demonstrates greater economic viability in areas with significant disparities in electricity pricing.

Droplet freeze desalination high fidelity modeling for sustainable water purification and diverse applications

Freeze desalination (FD) is an environmentally clean water purification technique that holds a great promise for low-energy consumption and with unlimited brine's salinity levels. The brine cooling induces freezing, rendering separation and removing contaminants. A high-fidelity molding using CFD is employed to explain the purification of ice from saline droplets in a sub-cold environment under natural free-convection. Comparisons were made with analytical predictions derived from experimentally acquired data through brine cooling in bulk and droplet scales. The procedural sequence employed facilitated the model's ability to accurately represent the ion diffusion and phase-change phenomena across various temperatures (−15 °C and − 25 °C), concentrations, partition & heat-transfer coefficients, and droplet volumes (3 μL to 9 μL). The salt concentration ranged from seawater (35 g/L) to RO (70 g/L) salinity levels. The model successfully accommodates the experimental temperatures observed during the equilibrium between the solid and liquid phases. The achieved desalination efficiency ranges from 20 % to above 40 %. Lastly, machine learning is implemented to identify the principal experimental parameters influencing desalination efficiency. In the suggested system, dynamic salinity/impurity and temperature profiles enable natural free convection brine cooling research. The current framework can study the purification/concentration efficiency of diverse range of mixtures subjected to freeze crystallization.

An investigation of a proposed freezing desalination system integrating sweating effect and a Centrifugal-Based brine rejection technique

Freeze desalination (FD) presents a promising yet underutilized technique for addressing global water scarcity, hindered by challenges such as the necessity for ice crushing and washing. This study introduces an innovative FD system incorporating sweating effects and centrifugal brine rejection, aiming to simplify the process by eliminating these additional steps. We evaluate the impact of key variables including sweating period, centrifugation duration, and rotational velocity on ice quality and process efficiency. Through systematic examination, our findings reveal that the sweating period significantly influences product salinity and salt rejection efficiency, achieving a salinity reduction from 40 ppt to 0.99 ppt with a 95.05 % salt rejection rate. Additionally, the centrifugation method showcased low power consumption, marking a significant advancement towards more sustainable desalination practices. This research not only demonstrates the feasibility of the proposed FD system but also sets the groundwork for future enhancements in the field of desalination technology.

Oilfield Brine as a Source of Water and Valuable Raw Materials—Proof of Concept on a Laboratory Scale

Oilfield brine is the largest byproduct stream generated during the extraction of crude oil and natural gas and may be considered a resource for the production of potable water and valuable raw materials. The high salinity of such waters limits the application of typical membrane-based techniques. In most oilfields, waste cold energy from the process of the low-temperature separation of natural gas is available and may be used as a source of cold for the freezing desalination (FD) of brine. As a result of the FD process, two streams are obtained: partially desalinated water and concentrated brine. The partially desalinated water may be suitable for non-potable applications or as a feed for membrane desalination. The concentrated brine from the FD could be used as a feed for the recovery of selected chemicals. This paper focuses on verifying the above-described concept of the freezing desalination of oilfield brine on a laboratory scale. The brine from a Polish oilfield located in the Carpathian Foredeep was used as a feed. Four freezing–thawing stages were applied to obtain low-salinity water, which subsequently was treated by reverse osmosis. The obtained permeate meets the criteria recommended for irrigation and livestock watering. The concentrated brine enriched with iodine (48 mg/L) and lithium (14 mg/L) was subjected to recovery tests. Ion exchange resin Diaion NSA100 allowed us to recover 58% of iodine. Lithium recovery using Mn- and Ti-based sorbents varies from 52 to 93%.

Numerical simulation of dynamic layer freeze desalination within an indirect contact freeze crystallizer

In the current study, a dynamic layer freeze desalination system is simulated numerically. The computational domain is a two-dimensional rectangular channel which contains inlet and outlet flows, and the simulation is performed using computational fluid dynamics. A pre-concentrated mixture is considered as the feed solution with an initial temperature and concentration of 257 K and 0.2 kg/kg, respectively. In this work, since the simulation parameters such as temperature and species mass fraction have high importance across the entire domain, the k–ω shear stress transport turbulence model was selected. A parametric study on the effect of the heat flux of the cold wall on the ice salinity and desalination rate is performed using three cases with heat fluxes of −1000, −1500, and −3000 Wm−2. It is observed that the ice generation speed in the case with a heat flux of −3000 Wm−2 is 3.28 times greater compared to the case with −1000 Wm−2 and its desalination rate is only 2.59% lower. The effect of the inlet velocity on the mentioned parameters is also investigated. It is observed that the cases with turbulent flow have approximately 19% and 23% lower ice salinity compared to the case with laminar flow.

Productivity Prediction for the Progressive Freeze Desalination Process Using Heat and Mass Transfer Modeling

AbstractPredicting the productivity of the freeze desalination process is of key importance. This paper describes an analytical method to predict the productivity for the progressive freeze desalination process utilizing the rectangular channel crystallizer design. The mass of ice produced during the process is considered a measure of productivity. The model was developed using heat and mass transfer modeling. The effect of coolant temperature (from −8 to −16 °C), liquid flow rate (4400–6000 mL min−1), and initial salt concentration of the liquid (1.5–7 wt%) on the mass of ice produced was investigated. The analytical results of the mass of ice produced were compared with the experimental data. A plausible match was found between the analytical and experimental results, with an error range between 6 % and 9 %. The model can predict the mass of ice produced for given values of the initial salt concentration of the liquid, initial mass of the liquid, salt concentration of thawed ice, liquid flow rate, and coolant temperature.

Interfacial ice sprouting during salty water droplet freezing

Icing of seawater droplets is capable of causing catastrophic damage to vessels, buildings, and human life, yet it also holds great potential for enhancing applications such as droplet-based freeze desalination and anti-icing of sea sprays. While large-scale sea ice growth has been investigated for decades, the icing features of small salty droplets remain poorly understood. Here, we demonstrate that salty droplet icing is governed by salt rejection-accompanied ice crystal growth, resulting in freezing dynamics different from pure water. Aided by the observation of brine films emerging on top of frozen salty droplets, we propose a universal definition of freezing duration to quantify the icing rate of droplets having varying salt concentrations. Furthermore, we show that the morphology of frozen salty droplets is governed by ice crystals that sprout from the bottom of the brine film. These crystals grow until they pierce the free interface, which we term ice sprouting. We reveal that ice sprouting is controlled by condensation at the brine film free interface, a mechanism validated through molecular dynamics simulations. Our findings shed light on the distinct physics that govern salty droplet icing, knowledge that is essential for the development of related technologies.

A gravity-induced desalination technology effectively improving the freshwater production efficiency of freeze desalination

Low desalination efficiency and water production efficiency limit the commercial application of freeze desalination (FD) technology. In this study, three freezing temperatures were set to carry out single-stage progressive freezing desalination of brackish water in southern Xinjiang, China. The ice were melted using conventional methods and gravity-induced desalination (GD), and the salt migration law during the icing and melting process was studied. The effect of GD technology on the improvement of the output of frozen desalinated produced water was quantitatively analyzed using scenario simulation. Experimental results showed that salts accumulated towards concentrated water during FD process. The ice total dissolved solids (TDS) increased with decreasing freezing temperature, which was linearly and positively correlated with the raw water TDS. GD efficiency was significantly affected by the salt concentration of ice crystals. In the first stage (the first 450 mL), ice-melt water was salt explosive dissolution, with salt drained mass accounted for more than 85% of the total salt mass. During GD process, exponential decay of ice-melt water TDS (TDSI) was observed with increasing ice-melt water amount. Through the simulation of the two exponential equation scenarios, it was found that Scenario II (mixed water TDSI as the target value) had significantly higher water yield and production rate than Scenario I (TDSI as the target value), with an increase of more than 23%. The algebraic relationship between TDSI of mixed water and the amount of ice-melt water was derived. GD technology can effectively improve the freshwater output efficiency of the FD process, which is manifested by the fact that the ice crystals of the FD process cannot produce freshwater using conventional melting. Scenario II can produce freshwater as high as 69.83% of the total amount of the GD ice-melt water. The GD technology performed increased multiplicatively in WPdv (decrease in water production) and WPRdv (decrease in water production rate) when the TDSI of the mixed water demanded by the user was low. When FD and GD are combined to desalinate salt water, lowering the freezing temperature can significantly increase the freshwater yield, breaking the limitation of freezing temperature for FD. Therefore, an automated, energy-saving freeze desalination-gravity desalination device capable of realizing the collection of the product water according to the users' needs was conceptualized. This study provides new ideas and algorithms for accurately assessing the efficiency of water production in the combined desalination of saltwater by FD and GD.

Thermochemical modeling and performance evaluation of freeze desalination systems

Freeze desalination (FD) is a method in which saline water is cooled below its freezing point and freshwater is separated from the brine in the form of ice crystals. FD is relatively insensitive to the salinity of the feed solution, making it suitable for desalination of high concentration brines such as the brine rejected from the seawater desalination plants. The design of the FD system and the thermochemical behavior of the brine upon freezing are critical factors in the energy performance of this method. To date, thermochemical properties of the concentrated seawater during cooling, such as the threshold of formation of ice and salt-hydrates and their corresponding cooling load of formation, are not well known. Likewise, the optimal configuration of the FD system to achieve the maximum energy efficiency has not been investigated. This work provides comprehensive data about the cooling load of freezing of concentrated brine rejected from seawater desalination plants along with the threshold of formation of ice and salt-hydrates backed-up by validation. Furthermore, the optimal configuration of the FD system is identified and the effects of the compressor isentropic efficiency and effectiveness of the system's heat exchangers on the work consumption of the FD system were investigated.

Towards spatiotemporal-resolved spectroscopic measurement of freezing desalination using femtosecond laser filaments

Freezing desalination can produce freshwater from seawater or industrial wastewater by ice crystallization with low energy consumption and less corrosion, and is promising for alleviating current stress on the world's water supply. However, the salt rejection dynamics during the freezing process is less understood due to the lack of real-time, high spatiotemporal-resolved detection methods. Here we present a proof-of-principle, quantitative, and simultaneous multi-salt detection approach for the measurement of salt rejection dynamics in salt-contaminated water at the ppm level using an ultrashort-pulsed femtosecond laser propagating in the filamentation regime. We show that this approach of filament-induced plasma spectroscopy possesses the abilities for both monitoring the change of salt concentration in the remaining unfrozen water during the freezing process and imaging the spatial concentration distributions of metal contaminants on the resultant ice surface. With this approach, we find that the initial salt concentration in water plays an essential role in the efficiency of the freezing desalination process, which shows a metal-species-dependent characteristic. Our results pave the way towards real-time, online, and high spatiotemporal-resolved detection of salt rejection dynamics of freezing desalination by ultrashort-pulsed lasers.

Experimental and theoretical study of a novel freeze desalination system with an intermediate cooling liquid

Freeze desalination (FD) is a potentially suitable method for treatment of high salinity brines. In this study, a novel FD system utilizing an intermediate cooling liquid (ICL) is fabricated and employed to desalinate brines with salinities up to 100,000 ppm. The FD system consists of a refrigeration unit and a desalination unit that are in thermal communication via the ICL. The desalination unit includes a freezing chamber, several filters, and a centrifugal separator. Feed brine is injected into the cold ICL inside the freezing chamber and partially freezes. The ice is subsequently separated from the ICL and unfrozen concentrated brine. The collected ice contains small amounts of concentrated brine, most of which is drained centrifugally before melting the ice. The developed FD system operates at atmospheric pressure and benefits from the superior heat transfer rates offered by direct contact between the brine and the cooling fluid. Furthermore, it resolves the issues of ice attachment to the cooling surfaces and mixing of refrigerant with the treated water. The effects of the feed brine salinity, cooling temperature, and centrifugation time on the recovery ratio and purity of the treated water were investigated experimentally. Results showed that the recovery ratio increases by decreasing the cooling temperature, and by decreasing the feed brine salinity. However, higher recovery ratios were found to increase the residual salinity in the treated water. For a feed brine with total dissolved solids (TDS) of 70,000 ppm and cooling temperature of −17 °C, recovery ratio of about 50 % and treated water TDS of ⁓2600 ppm were achieved experimentally. A theoretical model of the system was also developed and validated against the experimental results.

Performance Analysis and Multi-Objective Optimization of a Cooling-Power-Desalination Combined Cycle for Shipboard Diesel Exhaust Heat Recovery

This study presents a novel cooling-power-desalination combined cycle for recovering shipboard diesel exhaust heat, integrating a freezing desalination sub-cycle to regulate the ship’s cooling-load fluctuations. The combined cycle employs ammonia–water as the working fluid and efficiently utilizes excess cooling capacity to pretreat reverse osmosis desalination. By adjusting the mass flow rate of the working fluid in both the air conditioning refrigeration cycle and the freezing desalination sub-cycle, the combined cycle can dynamically meet the cooling-load demand under different working conditions and navigation areas. To analyze the cycle’s performance, a mathematical model is established for energy and exergy analysis, and key parameters including net output work, comprehensive efficiency, and heat exchanger area are optimized using the MOPSO algorithm. The results indicate that the system achieves optimal performance when the generator temperature reaches 249.95 °C, the sea water temperature is 22.29 °C, and 42% ammonia–water is used as the working fluid. Additionally, an economic analysis of frozen seawater desalination as RO seawater desalination pretreatment reveals a substantial cost reduction of 22.69%, showcasing the advantageous features of this proposed cycle. The research in this paper is helpful for waste energy recovery and sustainable development.

Evaluation of the energy consumption of hybrid desalination RO‐MED‐FD to reduce rejected brine

AbstractThe escalating global capacity of desalination plants has posed a significant environmental threat due to the discharge of brine. Consequently, urgent treatment of these hypersaline brines has become imperative. This article provides an overview of a novel hybrid model for water desalination. Energy consumption and brine discharge of three desalination configurations, namely freeze desalination (FD), multi‐effect desalination (MED), and reverse osmosis (RO), are compared. The configurations encompass FD, MED‐FD, and RO‐MED‐FD, with FD utilizing the brine from MED and RO desalination. The hybrid desalination system integrates with combined power and cooling CO2 system (CPCS‐CO2) for energy supply. This hybridization offers enhanced operational flexibility, increased desalination capacity, and reduced brine discharge. Optimal gas heater pressure exists for different temperatures and salt concentrations in saline water. The findings demonstrate a noteworthy 47% and 50% reduction in energy consumption and brine discharge, respectively, in RO‐MED‐FD compared to simple FD.