In the process of desalination by indirect freezing, ice formed on the cooled surface contains impurities due to kinetic effects. Sweating is an efficient method by which ice layer is purified under ...the effect of temperature gradient. The main kinetic parameters influencing sweating of ice are initial concentration of ice, sweating temperature and sweating time. In the present work, the effects of these parameters were studied using an experimental design. A statistical model for ice weight and ice purity was developed. The graphical representation of this model in the space of the variables enabled optimization of the whole desalination process time, which led to ice salinity less than the drinking water standards (0.5g/kg).
►Layer melt crystallization was applied to seawater desalination. ►The process involves two consecutives steps: freezing and sweating. ►Sweating has enabled the obtention of ice with low salt concentration, satisfying standards of potability. ►Optimal operating conditions are proposed by means of an experimental design.
This work aims at developing a dynamic layer crystallizer operated batchwise, for freezing desalination of sea water. The experiments were performed with water/NaCl solutions and with samples of sea ...water from Nice, Rabat and Marseille. The pilot crystallizer consists of a cooled tube immersed in a cylindrical double jacketed tank. The solution is poured into the tank and the crystallization takes place on the external surface of the tube, by applying a cooling ramp in the tube. The solution is agitated by air bubbling. The whole process involves the freezing step, leading to the crystallization of the ice layer and the sweating step, which consists of purifying in depth the ice layer by melting the impure zones. A parametric study on the effect of the operating parameters has allowed quantifying the role of the different key parameters of the freezing and sweating steps. Three experiments allowed reaching salinities lower than 0.5g/kg, satisfying the standards of drinking water. The duration of the whole process dropped to only 8h (5h for freezing and 3h for sweating), with a yield of sweating equal to about 50%, provided severe conditions were applied for sweating. Higher yields required longer times. Overall, the results show the feasibility of the technique.
► Initial temperature, ice growth rate and solution salinity are the parameters affecting ice purity. ► The sweating step is able to efficiently complete the purification. ► The duration of the whole process dropped to only 8h (5h for freezing and 3h for sweating).
•A process integrating block freeze concentration and precipitation is proposed.•Initial concentration and thawing rate influence the block freeze concentration.•Phosphorus and fluoride were ...separated in the first and second thawed fractions.•Thawing led to the recovery of pure water in the last thawed fraction.•Calcium fluoride, fluorapatite, and hydroxyapatite were produced by precipitation.
The work aims at developing a process for treating industrial wastewater from phosphoric acid and fertilizer production units by a coupled block freeze concentration-precipitation process. First, the block freeze concentration study, carried out on synthetic phosphoric acid solutions of concentrations ranging between 1.31 wt% 29.93 wt%, has shown that the purity of the ice block is strongly dependent on the initial concentration, the freeze duration, the thawing rate and the ice block temperature. Second, the block freeze concentration study, performed on a solution containing an orthophosphate-fluoride mixture, showed that the process increased the purity of the ice by the migration of occluded fluoride and orthophosphate ions until reaching a removal efficiency of F− and PO43− upper than 94 %. Further treatment by precipitation was studied on the first thawed fraction resulting from the freezing step. The results of the recovered liquid confirmed that, in the pH range between 2.4 and 12.73, the removal of fluoride and orthophosphate increased from 9.8 % to 96 % and from 6.3 % to 99 %, respectively. Precipitates characterization using methods such as X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy combined with energy dispersive X-ray analysis, indicated that CaF2, Ca5(PO4)3(OH)F and Ca5(PO4)3(OH) were successfully produced.
Desalination reverse osmosis reject brine-based porous geopolymer (RO/GP) was produced and investigated as an improved adsorbent for phosphorus (P) removal from tainted seawater, brackish water, ...river water, and municipal wastewater effluent. The RO reject brine/geopolymer was produced by reacting metakaolin and fly ash with a Na-alkali activator and anhydrous RO brine as a sacrificial template. The influence of RO reject brine content on water absorption, porosity, mechanical, and structural properties were examined. The developed RO-based geopolymers exhibited the greatest porosity (58.3–84.2 % vol%), a significant ratio of open porosity to total porosity (67.7–92.1 %), and outstanding compression strength (3.6–10.4 MPa). The produced RO/GP structure has an adsorption capacity of 92.4 mg-P/g. The sequestration reaction of phosphorus by RO/GP is of pseudo-second-order kinetic behavior via Chi-squared (χ2), RMSE, and determination coefficient (R2) values. Regarding their agreement with Langmuir behavior, the phosphorus adsorption uptakes occur in homogeneous and monolayer states. The reaction is exothermic, spontaneous, and favorable. The RO/GP exhibits significant affinity for phosphorus co-existing with Cl−, Na+, SO42−, K+, HCO3−, and Ca2+. The RO/GP shows high safety during the adsorption investigation, with a total cost of 0.32 $/kg-P.
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•RO reject brine as a precursor of porous alkali-activated materials.•Highly porous building geopolymers were obtained with porosity from 58.3 to 84.2 % vol%.•RO/GP was applied to remove phosphate ions from contaminated real aqueous media.•The maximum phosphate uptake capacity of RO/GP was 92.4 mg/g.•RO/GP has prospective safety and feasibility as a promising material for phosphate ions removal from contaminated media.
•Methodology to build phase diagram.•Whole milk/water phase diagram.•Determination by cryomicroscopy of the collapse temperature.
The state diagram is a key parameter when optimizing a freeze-drying ...cycle, as it allows us to set the optimum processing temperature for a specific product. The purpose of this work is to provide some thermodynamic and physicochemical data for optimizing the freeze-drying cycle of whole milk. Freezing point measurements were determined using differential scanning calorimetry and cryoscopy methods, and glass transitions were evaluated by DSC. The endothermic peak was used as the equilibrium freezing point, a variation from 273.93 K to 264.92 K was detected when the dry matter content varied from 0 to 75%. Tg midpoint temperature was used as glass transition of dry mater. Furthermore, Fox and Gordon-Taylor equations were used to predict the glass transition curve to determine Tg', this temperature was used as an approximation of the critical temperature Tc. Collapse temperature was determined using the freeze-drying microscopy setup.
Study of a Melt Crystallization Process for Seawater Desalination Anouar Rich Mostapha Siniti Denis Mangin Jean-Paul Klein Youssef Mandri Tijani Bounahmidi Ahmed Bouhaouss Stephane Veesler Mohamed El Ganaoui
Journal of mechanics engineering and automation,
01/2015, Letnik:
5, Številka:
1
Journal Article
Odprti dostop
The work aims to develop a process for freezing desalination of seawater on cold walls. The experiments were performed with water/NaCl solutions of different concentrations and with samples of ...seawater. The pilot crystallizer consists of a cooled tube immersed in a cylindrical double jacketed tank containing water to be treated. The complete process of desalination is conducted in two steps： the freezing step, leading to the crystallization of the ice layer and the sweating step, which consists of purifying the ice layer in depth by melting the impure zones. The systematic study of the influence of operating parameters has highlighted the important role of the cooling ramp and salinity of the solution on the purity of the ice produced. In the absence of stirring, the temperature of the double jacket also has a noticeable effect on the purity of the ice due to temperature gradients, and consequently, convection currents that may result in the solution. The results of this work show the feasibility of the technique and give a good indication of operating conditions that can be used to produce drinking water.
Reject desalination brine is a rich source of salts and valuable materials. But, its disposal into the external environment generates a major source of pollution. This paper investigated the ...production of reactive CaO from reverse osmosis (RO) reject brine and its use as adsorbent for phosphate removal from contaminated seawater and RO industrial waste. This study was realized via two steps. Firstly, the recovery of Ca-phase from reject brine via oxalic acid at optimized conditions resulting clcium oxalate monohydrate, and its calcination at 900°C for 2 h to produce the reactive CaO. Secondly, the produced reactive CaO was doped by Fe3O4 via co-precipitation method to produce reactive CaO@Fe3O4 composites. The reactive CaO@Fe3O4 was explored as a potential adsorbent with enhanced capacity for phosphate ions (PO43−) removal. The estimated maximum reactive CaO@Fe3O4 uptake capacity for PO43− (106.3 mg/g) is comparatively higher than the identified values for the reactive CaO (72.8 mg/g) and Fe3O4 (41.6 mg/g). The kinetics of the PO43− uptake reaction via reactive CaO@Fe3O4 obey the Pseudo-Second order model (R2 > 0.98) and the equilibrium time was determined after 450 min. The equilibrium study of the demonstrated reaction exhibited excellent agreement with the isotherm assumption of the Freundlich model implying multilayer and heterogeneous adsorption processes. The thermodynamic aspect of PO43− adsorption reaction is favorable and exothermic. The adsorbent selectivity, reusability experiments and realistic study were also discussed . Furthermore, the computational study using DMs was applied to better understand the interaction for {PO43−/CaO(111)&CaO@Fe3O4(111)} systems. The simulation results demonstrate favorable, more stable, spontaneous adsorption and exothermic for PO43−/CaO@Fe3O4(111) than PO43−/CaO(111)complex. Overall, CaO@Fe3O4(111) could serve as a effective and reusable adsorbent for phosphate ions recovery from aqueous solutions.
Le travail vise à développer un procédé de dessalement de l’eau de mer par congélation sur parois froides. L’étude thermodynamique a permis de quantifier l’effet de la composition et de la salinité ...de l’eau sur la température de congélation et la température de précipitation de Na2SO4,10 H2O. Les résultats sont bien décrits par le code de calcul de Frezchem, dérivé du modèle de Pitzer. Les essais de dessalement par congélation ont été conduits avec des solutions eau/NaCl de différentes concentrations, ainsi qu’avec de l’eau de mer de Rabat, Nice et Marseille. Le montage expérimental mis au point se compose d’un doigt de gant plongé dans une cuve double enveloppée contenant l’eau à traiter. Le procédé complet de dessalement est conduit en deux étapes: l’étape de congélation produisant un dépôt de glace sur le doigt de gant et l’étape de ressuage, effectuée après vidange de la saumure, qui consiste à purifier en profondeur la glace en opérant une fusion des zones impures. Une caméra filme la couche de glace et fournit la cinétique de croissance de la couche. La congélation a été effectuée dans une solution stagnante ou dans une solution agitée par injection d’air. Elle est conduite en appliquant deux rampes de refroidissement, respectivement dans le doigt de gant et dans la double enveloppe, qui peuvent être ou non identiques. Les essais ont montré la nécessité d’ensemencer la couche de glace sur le tube et d’ajuster finement la température initiale de la rampe de refroidissement. L’étude systématique de l’influence des paramètres opératoires a mis en évidence les rôles importants de la rampe de refroidissement et de la salinité de la solution sur la pureté de la glace produite. En l’absence d’agitation, la température de la double enveloppe a également un effet notoire sur la pureté de la glace à cause des gradients de température, et par suite, des courants de convection qu’elle peut engendrer au sein de la solution. En régime agité, la solution semble être à chaque instant en équilibre avec la glace. Une même salinité finale de la glace peut être obtenue avec des rampes de refroidissement beaucoup plus rapides qu’en statique. Quelles que soient les performances de la congélation, le ressuage est ensuite indispensable pour atteindre la norme de potabilité. La recherche de conditions opératoires optimales a permis de réduire la durée du procédé global à 8h (5h de cristallisation et 3h de ressuage). Les résultats de ce travail montrent la faisabilité de la technique et donnent une bonne idée des conditions de fonctionnement qui peuvent être employées pour produire l'eau potable
The work aims to develop a process for freezing desalination of seawater on cold walls. The thermodynamic study has quantified the effect of composition and of salinity on the freezing temperature and the precipitation temperature of Na2SO4,10 H2O. The results are well described by the calculation code Frezchem, derived from the model of Pitzer. The experiments were performed with water/NaCl solutions of different concentrations and with samples of sea water from Nice, Rabat and Marseille. The pilot crystallizer consists of a cooled tube immersed in a cylindrical double jacketed tank containing water to be treated. The complete process of desalination is conducted in two steps: the freezing step, leading to the crystallization of the ice layer and the sweating step, which consists of purifying in depth the ice layer by melting the impure zones. A camera films the ice and provides the growth kinetics of the layer. Freezing was performed in a stagnant solution to a stirred solution or by injecting air. It is conducted by applying two cooling ramps, respectively in the tube and the double jacket that may or may not be identical. Tests have shown the need to seed the ice on the tube and fine-tune the initial temperature of the cooling ramp. The systematic study of the influence of operating parameters has highlighted the important role of the cooling ramp and salinity of the solution on the purity of the ice produced. In the absence of stirring, the temperature of the double jacket also has a noticeable effect on the purity of the ice due to temperature gradients, and consequently, convection currents that may result in the solution. Steady stirring, the solution seems to be at all times in equilibrium with ice. Same final salinity of the ice can be obtained with ramps cooling much faster than static. Whatever the performance of the freezing, the sweating is then necessary to meet the standard for drinking water. The search for optimum operating conditions has reduced the duration of the overall process to 8 hours (5 hours the crystallization and 3 hours of sweating). The results of this work show the feasibility of the technique and give a good indication of operating conditions that can be used to produce drinking water
This work aims in developing a static layer crystallizer for freezing desalination of sea water. The experiments were performed with a simple system of H(2)O-NaCl and with samples of sea water from ...Rabat. The pilot crystallizer consists in a tube cooled by means of a thermostatic bath. The tube is immerged in a cylindrical double jacketed tank cooled by means of a second thermostatic bath. The brine is poured into the tank and the crystallization takes place on the external surfacs of the tube. The global process is divided into 4 steps: (i) crystallization of the ice layer by controlling the cooling rate in the tube (ii) draining off the concentrated brine (iii) purification of the layer by sweating and (iv) melting of the ice to recover the fresh water. A parametric study of the effect of the operating parameters has allowed us to quantify the role of the different key parameters of the crystallization step. Within the studied domain, the purity of the crystalline layer was mainly affected by the initial salinity of the brine. The growth rate of the layer, controlled by the cooling rate in the tube, had also a significant effect. Experiments performed with Rabat sea water showed that a fresh water of salinity close to the drinking water standards could be obtained in one stage within 31 h. Desalination operated in two consecutive stages (10 h+11 h) gave salinity below the standards with a comfortable safety margin. If sufficiently severe operating conditions are applied, sweating is able to purify the interior of the ice layer and to reach the drinking water standards, provided the impurity concentration of the ice produced in the crystallization step is low enough. The mass loss induced by sweating is also high when the impurity concentration is high. These first results are promising and show the feasibility of the process which still requires to be optimized.
Le travail vise à développer un procédé de dessalement de l'eau de mer par congélation sur parois froides. L'étude thermodynamique a permis de quantifier l'effet de la composition et de la salinité ...de l'eau sur la température de congélation et la température de précipitation de Na2SO4,10 H2O. Les résultats sont bien décrits par le code de calcul de Frezchem, dérivé du modèle de Pitzer. Les essais de dessalement par congélation ont été conduits avec des solutions eau/NaCl de différentes concentrations, ainsi qu'avec de l'eau de mer de Rabat, Nice et Marseille. Le montage expérimental mis au point se compose d'un doigt de gant plongé dans une cuve double enveloppée contenant l'eau à traiter. Le procédé complet de dessalement est conduit en deux étapes: l'étape de congélation produisant un dépôt de glace sur le doigt de gant et l'étape de ressuage, effectuée après vidange de la saumure, qui consiste à purifier en profondeur la glace en opérant une fusion des zones impures. Une caméra filme la couche de glace et fournit la cinétique de croissance de la couche. La congélation a été effectuée dans une solution stagnante ou dans une solution agitée par injection d'air. Elle est conduite en appliquant deux rampes de refroidissement, respectivement dans le doigt de gant et dans la double enveloppe, qui peuvent être ou non identiques. Les essais ont montré la nécessité d'ensemencer la couche de glace sur le tube et d'ajuster finement la température initiale de la rampe de refroidissement. L'étude systématique de l'influence des paramètres opératoires a mis en évidence les rôles importants de la rampe de refroidissement et de la salinité de la solution sur la pureté de la glace produite. En l'absence d'agitation, la température de la double enveloppe a également un effet notoire sur la pureté de la glace à cause des gradients de température, et par suite, des courants de convection qu'elle peut engendrer au sein de la solution. En régime agité, la solution semble être à chaque instant en équilibre avec la glace. Une même salinité finale de la glace peut être obtenue avec des rampes de refroidissement beaucoup plus rapides qu'en statique. Quelles que soient les performances de la congélation, le ressuage est ensuite indispensable pour atteindre la norme de potabilité. La recherche de conditions opératoires optimales a permis de réduire la durée du procédé global à 8h (5h de cristallisation et 3h de ressuage). Les résultats de ce travail montrent la faisabilité de la technique et donnent une bonne idée des conditions de fonctionnement qui peuvent être employées pour produire l'eau potable
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