Eutectic Freeze Crystallization Research Articles

Evaluation of Experimental and Economic Potential of Industrial Borax Aqueous Solution by Eutectic Freeze Crystallization Method

Evaluation of Experimental and Economic Potential of Industrial Borax Aqueous Solution by Eutectic Freeze Crystallization Method

Phase diagrams of CoSO4-H2O and CoSO4-H2SO4-H2O systems for CoSO4·nH2O (n = 6,7) recovery by cooling and eutectic freeze crystallization

This paper reports the solid-liquid phase equilibria of the CoSO4-H2O and CoSO4-H2SO4-H2O systems at low temperatures. Binary and ternary phase diagrams, including the stable solid phases CoSO4·6H2O and CoSO4·7H2O were established using experimental data and thermodynamic modeling applying the mixed-solvent electrolyte (MSE) model. The results showed that the addition of H2SO4 shifts the eutectic temperature and concentration to lower values for cobalt sulfate and ice crystallization. The trends obtained from the experimental data and the modeling are consistent for the binary CoSO4-H2O system with good agreement, but the ternary CoSO4-H2SO4-H2O system shows some deviations. In general, the MSE model is shown to be reliable for inferring and establishing the phase diagram of the low-temperature system. The phase diagrams are helpful for designing the pathways of cooling crystallization and eutectic freeze crystallization and assessing the performance of the low-temperature crystallization process in the production of CoSO4 hydrates. In addition, some practical examples of cooling crystallization and eutectic freeze crystallization of CoSO4 solutions are provided.

APPLICATION OF EUTECTIC FREEZE CRYSTALLIZATION FOR WASTEWATER TREATMENT: A REVIEW

APPLICATION OF EUTECTIC FREEZE CRYSTALLIZATION FOR WASTEWATER TREATMENT: A REVIEW

Eutectic freeze crystallization in the boric acid–water system

Eutectic freeze crystallization in the boric acid–water system

Dynamic modelling and simulation of eutectic freeze crystallization process for recovery of ammonium sulphate from aqueous solutions

The advancement of industrial sectors generates large amount of wastewater containing ammonium sulphate (AS) ions, yet the current AS recovery technologies are energy-extensive and produce excessive sludge. In this study, a dynamic model for a batch crystallizer was developed to investigate the eutectic freeze crystallization process of AS in aqueous solutions using the method of moment (MoM). The variables affecting the crystal size distribution of AS and ice were described in terms of zeroth moment μ0, first moment μ1, second moment μ2 and third moment μ3. The μ0 of ice crystals increased significantly until 2 s and slowed down thereafter while μ0 of AS crystal increased steadily and reached a constant value of 1/m3s after 1 s. The μ1, μ2, and μ3 of the AS and ice crystals depicted a similar increasing trend. Through process optimization using a 3-D plot on the initial concentration of the system and initial temperature of cooling fluid which had been identified as the significant parameters via iterative plot using MATLAB software, the AS and ice reached maximum crystallization at 255 K which was close to the eutectic point of AS-water system at 254 K. The dynamic model which comprised of population, mass and energy balance equations established in this study demonstrated effectiveness in the prediction of crystallization of AS in aqueous solutions.

Novel materials and crystallizer design for freeze concentration

When wastewater streams or seawater are desalinated, the waste product is a hypersaline brine stream which is usually disposed of or stored in evaporation ponds. Eutectic Freeze Crystallization (EFC) is a novel treatment technology for these hypersaline brines that can recover both water and dissolved salts. It works by cooling the stream to the Eutectic temperature, at which point both ice and salt will crystallize. The ice, being less dense than the solution, floats, and the salt, being denser, will sink – thus effecting a gravity separation.Theoretically, EFC can result in zero liquid discharge (ZLD) and has several advantages over conventional separation techniques, including low energy consumption; high quality products and it requires no additional chemicals. It can also be combined with other separation technologies to optimise the separation process.Although it sounds simple, an EFC process can be difficult to design and operate effectively, since each of the elements has its own complexity. Specifically, the issue of ice scaling is one of the major challenges in implementing EFC.Therefore, in this study, we focussed on ice scaling in a freeze concentration system i.e ice crystallization only; without the salt crystallization component that would define the process as an EFC process.We investigated two approaches to scaling reduction:The first was modification of the heat exchanger surface, where we investigated the effect of three different heat exchanger surfaces on ice scaling: a novel polypropylene graphite (PP GR) material, Stainless Steel 316 (SS316) and Aluminium. These three materials were tested in a small-scale Column Crystallizer (CC).The second method was by designing a Continuously Stirred Column Crystallizer (CSCC), which aimed to improve the hydrodynamics independent of pumping, to improve on the heat and mass transfer distribution across the crystallizer and to improve product purity by providing a larger product separation zone. The focus was on producing an efficient crystallizer design, bearing current industrial implementation hurdles in mind.This study confirmed that using materials of low surface energy has the potential to increase the scaling induction times and reduce the severity of ice scaling, hence improving process efficiency. The outcome of the initial, small-scale study provided the required evidence to support scaling up the column crystallizer using PP GR as an HX material of choice.The study also showed that the unique multicompartment mixing system of the novel CSCC led to high supercoolings and long induction times being attained. The column design provides a larger disengagement zone than a conventional column, which has the potential to improve the separation efficiency, and hence the product purity.In summary, with the correct choice of heat exchanger material and appropriate crystallizer design, we have shown that one of the major challenges i.e. ice scaling, can be overcome. This paves the way for EFC being able to be used for the treatment of hypersaline brines, not only at laboratory scale, but also at larger, commercial scales.

Using of saltwater to increase the output power of a steam injected gas turbine (STIG) by connecting spray freezing desalination to it

Gas turbines are one of the common methods for generating electrical energy. However, reducing the output power by increasing the air temperature is one of the problems of these turbines. Common methods to compensate for the power drop of gas turbines are often based on turbine inlet air cooling (TIAC) technology or injecting steam or water into the turbine as humidified gas turbine (HGT) that causes an increase in its output power. However, these technologies often require high consumption of fresh water which limits their use in dry and low-water areas. Therefore this study has investigated the connection of a spray freezing desalination to a steam-injected gas turbine (STIG) through a reverse Brayton cycle for increasing its output power by consuming saltwater. This spray freezing desalination is a process based on eutectic freeze crystallization (EFC) technology that uses compressed air in a turbo expander to produce chilled air that can crystallize the droplet of sprayed saline water. This desalination technology has the potential of zero liquid discharge (ZLD). Therefore, with the possibility of using a saline water source such as reverse osmosis (RO) brine in this process, in addition to increasing the output power of gas turbines, it will be possible to reduce the environmental problems related to its disposal.

Scaling up continuous eutectic freeze crystallization of lactose from whey permeate: A pilot plant study at sub-zero temperatures

Eutectic freeze crystallization is explored as an alternative to the state-of-the-art evaporation process for the recovery of lactose from whey permeate. At the so-called eutectic freezing point, both water (the solvent) and lactose (the solute) crystallize and can be removed continuously while continuously feeding whey permeate. This continuous process is demonstrated on a pilot scale at sub-zero temperatures. In the first instance, only freeze concentration of whey permeate took place at −4 °C. It was possible to reach a lactose concentration of 30 wt% and hardly any nucleation was observed. The resulting ice had high purity, with a lactose concentration of ±2 wt%. Next, the eutectic phase was reached, and lactose and ice crystallized simultaneously and were continuously removed from the system, the resulting crystals had parallelogram morphology with an average size of 10 µm. Ice was recovered at a rate of 60 kg/h and lactose was recovered at a rate of 16 kg/h, yielding over 80% of the feed lactose. A conceptional design was proposed for an improved yield and reduction of energy. Yields of at least 80% and up till 95% could be achieved. Compared to the state-of-the-art mechanical vapor recompression (MVR), EFC is 80% more energy efficient.

Concentrating stabilized human urine using eutectic freeze crystallization for liquid fertilizer production

Resource recovery from source-separated urine can be used to produce fertilizers and provide a more sustainable alternative to mineral fertilizers. Reverse osmosis can be used to remove up to 70% of the water in urine that has been stabilized with Ca(OH)2 and pre-treated with air bubbling. However, further water removal is limited because of membrane scaling and equipment operating pressure limitations. A novel hybrid eutectic freeze crystallization (EFC) and RO system was investigated as a method to concentrate human urine, whilst simultaneously crystallizing salt and ice under EFC conditions. A thermodynamic model was used to predict the type of salts that would crystallize, their associated eutectic temperatures, and how much additional water removal was required (using freeze crystallization) to reach eutectic conditions. This innovative work showed that at eutectic conditions, Na2SO4∙10H2O crystallizes simultaneously with ice in both real and synthetic urine, thus providing a new method to concentrate human urine for liquid fertilizer production. A theoretical mass balance of a hybrid RO-EFC process, including ice washing and recycle streams, showed that 77% of the urea and 96% of the potassium could be recovered with a 95% water removal. The final liquid fertilizer would have a composition of 11.5% N and 3.5% K, and 3.5 kg of Na2SO4∙10H2O could be recovered from 1000 kg of urine. Over 98% of the phosphorus would be recovered as calcium phosphate during the urine stabilization step. A hybrid RO-EFC process would require 60 kWh m−3 of energy, which is substantially less than other concentration methods.

Design of a multistage hybrid desalination process for brine management and maximum water recovery.

Hypersaline brine production from desalination plants causes huge environmental stress due to the untenable conventional discharge strategies. Particularly, brine production is expected to drastically increase in the coming few decades due to the increasing desalination capacity in attempts of forestalling water scarcity. Thereby, zero liquid discharge (ZLD) is a worth-considering solution for strategic brine management. ZLD or minimal liquid discharge (MLD) systems provide maximum water recovery with least or zero liquid waste generation and valuable salt production. In this work, a theoretical design of ZLD/MLD system is proposed for reverse osmosis (RO) brine management. Different scenarios are investigated utilizing multistage freeze desalination (FD) and its hybridization with multistage direct contact membrane distillation (DCMD), and eutectic freeze crystallization (EFC) technologies. The design is based on the experimental assessment of the indirect FD process at different feed salinities, i.e., 2g/L to 155g/L. FD experiments showed that ice quality is reduced at greater crystallinity levels and initial concentration. Moreover, a computational fluid dynamics (CFD) model is utilized to assess the performance of DCMD. A single DCMD module could produce 53kg/(m2.h) of pure water operating with 69% thermal efficiency. Eventually, water recovery, water quality, as well as specific energy consumption (SEC) are evaluated for the whole system. Based on different configurations of the hybrid ZLD system, the proposed design can achieve water recovery between 40 and 93% with SEC range of 28-114 kWh/m3. Results also showed that the produced water quality exceeds drinkable water standards ( 500mg/L). This work has provided great evidence in the practicality of ZLD/MLD systems for sustainable brine management.

Effect of Heat Transfer Driving Force and Ice Seed Loading on the Production of Ice and Salt from a Dilute Brine Treated Using Eutectic Freeze Crystallization

Eutectic Freeze Crystallization (EFC) is a separation technology that separates solute from solvent by cooling the brine to a temperature below its eutectic point, such that ice and salt simultaneously crystallize out of the solution. Achieving consistent production of ice and salt at high production rates has been a challenge for EFC. This is due to heat transfer limitations, which are more severe when EFC is applied to dilute brines. This work investigated the effect of the heat transfer driving force, ΔTLMTD, and ice seed loading (SL) on the production of ice and salt from a dilute brine. A 1.45 L stirred crystallizer was used for the experiments at varying coolant temperatures to investigate the effect of ΔTLMTD, and at varying seed masses to investigate the effect of seed loading. It was found that, as the ΔTLMTD increased, the yield of ice and salt increased. This was attributed to the increase in the heat transfer rate as ΔTLMTD and heat transfer rate are directly related. The ice yield was divided between ice in suspension and ice formed on the wall (scale layer), with a majority of the total ice yield being scale ice. Increasing the seed loading (SL) increased the yield of ice in suspension and decreased the yield of scale ice. The seeds allowed for increased surface area for crystallization in the bulk. This allowed for most of the supersaturation to be consumed in the bulk, leaving little supersaturation for crystallization at the wall. This reduced the propensity for scale formation. The reduction in the scale layer increased the heat transfer rate between the bulk and the coolant, allowing for more ice to be formed in suspension.

Towards sustainable production of minerals and chemicals through seawater brine treatment using Eutectic freeze crystallization and Electrodialysis with bipolar membranes

European policy encourages the adoption of sustainable systems that promote the efficient use and recovery of minerals and chemicals. In this respect, desalination brines do contain a dramatic amount of valuable minerals and can be valorized through appropriate treatments rather than releasing them into the environment. This paper proposes an innovative brine recovery system for obtaining high purity chemicals through the integration of Eutectic Freeze Crystallization (EFC) and Electrodialysis with Bipolar Membrane (EDBM) technologies. Two separate laboratory-scale experimental campaigns were carried out to validate the potential integration of the two processes. Mirabilite (Na2SO4∙10H2O) has been recovered with a purity of 99.9% using the EFC, and a feed rich in NaCl with low impurities has been further processed in an EDBM unit. EDBM tests with feed solutions simulating EFC effluents have shown that it is possible to produce acidic and basic solutions with high purity (>99%), despite the presence of impurities in the feed. Interestingly, the low EDBM specific consumptions of 0.9–1.1 kWh kg−1NaOH at 100 A m−2 and 1.3–1.6 kWh kg−1NaOH at 300 A m−2 were comparable with and without impurities. In the context of the circular economy strategy promoted by the EU-H2020 Water Mining project, the current study demonstrates that this integrated system effectively minimizes waste, promoting sustainability while providing a potential economic return.

Challenges in preparing for Environmental Technology Verification in a demonstration project: A case study of three innovative water treatment technologies

The European Union's Environmental Technology Verification (ETV) program aims to foster innovative environmental technologies to reach the market and reassure potential users. This paper presents an investigation of using ETV for three technologies, being developed within the EU Zero Brine research and innovation project. The technologies were designed to recover high quality water, salts and minerals from brine solutions. The technologies in focus are the forward feed MED evaporator, the Multi Feed – Plug Flow Reactor Crystalliser and Eutectic Freeze Crystallization. The study sought to understand the challenges of the ETV process, the readiness and eligibility of technologies, and possible preparations within the project lifetime. Challenges identified included: understanding what sufficient market readiness is, and achieving this within the duration of a project (also linked to funding allocation for the ETV process); and developing suitable performance claims, supported with sufficient levels of test data. A simple framework is presented to aid the integration of ETV into the development process. It promotes the use of life cycle assessment to understand the environmental added value of the technology and aid the development of performance claims.

Gypsum Seeding to Prevent Scaling

Eutectic freeze crystallization (EFC) is a novel separation technique that can be applied to treat brine solutions such as reverse osmosis retentates. These are often a mixture of different inorganic solutes. The treatment of calcium sulphate-rich brines using EFC often results in gypsum crystallization before any other species. This results in gypsum scaling on the cooled surfaces of the crystallizer, which is undesirable as it retards heat transfer rates and hence reduces the yield of other products. The aim of this study was to investigate and understand gypsum crystallization and gypsum scaling in the presence of gypsum seeds. Synthetic brine solutions were used in this research because they allowed an in-depth understanding of the gypsum bulk crystallization process and scaling tendency without the complexity of industrial brines. A cooled, U-shaped stainless-steel tube suspended in the saturated solution was employed as the scaling surface. This was because a tube-shaped surface enabled the introduction of a constant temperature cold surface in the saturated solution and most industrial EFC crystallizers are constructed from stainless steel. Gypsum seeding was effective in decreasing the mass of scale formed on the heat transfer surface. The most effective seed loading was 0.25 g/L, which reduced scale growth rate by 43%. Importantly, this seed loading is six times the theoretical critical seed loading. The seeding strategy also increased the gypsum crystallization kinetics in the bulk solution, which resulted in an increase in the mass of gypsum product. These findings are relevant for the operability and control of EFC processes, which suffer from scaling problems. By using an appropriate seeding strategy, two problems can be alleviated. Firstly, scaling on the heat transfer surface is minimised and, secondly, seeding increases the crystallization kinetics in the bulk solution, which is advantageous for product yield and recovery. It was also recommended that the use of silica as a seed material to prevent gypsum scaling should be investigated in future studies.

Eutectic freeze crystallization for recovery of NiSO4 and CoSO4 hydrates from sulfate solutions

In this study, eutectic freeze crystallization (EFC) was investigated to recover NiSO4 and CoSO4 hydrates from aqueous and dilute sulfuric acid solutions of metal sulfates. Binary phase diagrams were established using a combination of thermodynamic modeling and experimental data. The mixed-solvent electrolyte (MSE) model was employed to model solid–liquid phase equilibria. The predicted binary phase diagrams from the model were in good agreement with the experimental results. Experimental eutectic temperatures and eutectic metal sulfate concentrations for the NiSO4-H2O and CoSO4-H2O systems are −3.3 °C and 20.8 wt% and −2.9 °C and 19.3 wt%, respectively. For NiSO4-H2SO4-H2O and CoSO4-H2SO4-H2O systems, the eutectic temperature and eutectic metal sulfate concentration decrease with increasing H2SO4 concentration. Batch experiments were performed to study the EFC of different sulfate solutions, including 25- wt% NiSO4 in H2O, 20- wt% NiSO4 in 0.5 mol/kg H2SO4, 25- wt% CoSO4 in H2O, and 20- wt% CoSO4 in 0.5 mol/kg H2SO4. The results show that controlling the supersaturation allows high-quality ice and salt crystals to be recovered as separate phases under eutectic conditions, with the crystalline salts in the form of heptahydrates. This study shows that EFC can be a promising alternative to evaporative crystallization for recovering NiSO4 and CoSO4 hydrates from sulfate solutions.

A novel, in-situ observation of the initial ice scale layer development on different heat exchanger surfaces during EFC

Ice scale formation is one of the main impediments to the successful implementation of eutectic freeze crystallization (EFC). Controlling the formation of ice scale on heat exchanger (HX) surfaces has been attempted by using mechanical scrapers, with limited success in EFC. Some of these limitations have been associated with the HX surface properties. This has highlighted the requirement to understand the influence of HX surface properties on ice scaling to improve the control of ice scaling. This was achieved by using an augmented differential interference contrast (DIC) technique. The DIC technique allowed the observation of the development of the initial ice scale layer on four different HX surfaces which has not been observed previously. Ice scaling occured through the formation of distinct “ice islands” on the HX surfaces, showing different morphologies. These "ice islands" grew radially, ultimately merging to form the initial ice scale layer that is transparent to the naked eye. It was concluded that in the absence of bulk crystals, ice scaling occurs through heterogeneous nucleation followed by lateral and vertical growth. In the presence of bulk ice crystals, as was observed when a brass HX plate was used, scaling initiated through the adhesion of ice crystals onto the HX surface. Additional bulk ice crystals cohered onto the growing front of the ice scale, ultimately covering the entire HX surface. The scaling rates were influenced by a combination of both the nucleation and growth rates and differed with the HX materials resulting in different ice scaling rates. In conclusion, high scaling rates were attributed to high nucleation rates. When ice scaling was dominated by growth, the scaling rate was reduced. Overall, brass was found to delay scaling and increase the probability of bulk nucleation. SS316 was found to have the highest nucleation rate, resulting in the highest scaling rate of all the materials.

What to do with toxic, contaminated cellulose-based adsorbents

This editorial considers the end fates of toxic materials, such as heavy metals, dyes, and synthetic organic compounds, which can be recovered from polluted water by using bio-based adsorbents. The point of the editorial is that insufficient research attention has been paid to the final fate of such contaminants. By contrast, much is known regarding factors affecting the adsorption capacities and rates of adsorption onto cellulose-based materials. Highly contaminated solutions are produced during the regeneration of biosorbent materials. Eutectic freeze crystallization potentially could be used to isolate relative pure compounds of heavy metals from such solutions. Alternatively, biochar can be prepared from cellulosic material in such a way as to achieve strong attachment to certain pollutants. Such biochar, after its use as an adsorbent, could be placed in the ground, where it can be expected to remain stable as sequestered carbon. A high ion exchange capacity of such biochar has potential to reduce the rates of leaching, which could otherwise lead to contamination of groundwater near to landfill sites. As shown by these examples, some promising answers to the final fate of contaminants may conform to a “circular economy” model, whereas other promising answers may conform to a “cradle-to-grave” viewpoint.

Pilot studies on circular economy solution for the coal mining sector

The coal mining sector is being particularly affected by the saline waste waters problem. One of the possible solutions is to use the effluents as the source of raw materials: demineralized water, salt, magnesium hydroxide. This paper presents the results obtained in a pilot plant of capacity of 400 L/h, which was in operation for 9 months in the “Bolesław Śmiały” coal mine in Łaziska Górne, Poland. The coal mine water was being pre-treated with ultrafiltration and decarbonization and subjected to a two-pass nanofiltration, which splits the feed into two streams: salt-rich permeate, and calcium- and magnesium-rich retentate, which can be used for recovery of magnesium hydroxide by either conventional precipitation or by CrIEM technology. The nanofiltration permeate was concentrated in a hybrid reverse osmosis-electrodialysis system, producing demineralized water and highly saline concentrate, which could be used as a feedstock for salt production by either thermal crystallization or eutectic freeze crystallization.

A sub-zero crystallization process for the recovery of lactose

In industry, lactose is generally produced by concentrating whey permeate by evaporation followed by a slow cooling process where lactose is crystallized. Here, an alternative method is presented whereby the concentration and crystallization steps are combined at sub-zero temperatures, so-called eutectic freeze crystallization. It was discovered that simultaneous crystallization of lactose and water (ice) is possible. The obtained lactose crystals had an average size of 10 μm and a thin triangular or tomahawk morphology. The process was analyzed in detail in two steps: freeze concentration and lactose crystallization at sub-zero temperatures. Freeze concentration experiments showed that concentrating to supersaturation was possible without excessive lactose crystallization. In the second step, lactose was crystallized at temperatures below zero from a 30 wt% lactose solution, without observation of significant primary or secondary nucleation. The amount of seed material had a large influence on the final yield, crystal size and morphology. The optimum seed amount was found to be at 0.08% of the total lactose; the resulting crystals had an average size of 26 μm and a tomahawk morphology. Although highly supersaturated conditions are present in the sub-zero crystallization of lactose, crystal growth is found to be the predominant process rather than nucleation.

Eutectic freeze crystallization: application, process design and future potential

This paper aims to analyze the process of eutectic freeze crystallization, as well as its current use and future potential. The fundamental concepts of this process and the equipment required are studied to ascertain its advantages compared to conventional separation methods such as evaporative crystallization and reverse osmosis. Various equipment or combinations of equipment are also evaluated in terms of energy requirement and cost in order to optimize eutectic freeze crystallization based on situational conditions. By looking at current industrial applications of eutectic freeze crystallization, the future of this process and its feasibility in larger scale productions can be determined. Lastly, an in-depth analysis is carried out on the use of eutectic freeze crystallization in Kemira Chemical Plant and DWP Botlek of Evides Industriewater to improve the understanding of this process in a real industrial setting.