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Magnesium is one of the eight most abundant elements on the world and the third most abun- dant in the sea, buc practically only two countries (Russia and China) control the world market for this compound. Product purity, Mg recovery, crystal morphology and granulometric distribution of precipitated particles were examined through careful laboratory analysis and results from different tests were compared, in order to identify the effect of allcaline species’ nature and concentration on precipitation phenomena.

In this paper a dynamic model for the MED-TVC process has been developed and valided by a comparison with data from a real plant situated in Trapani, Italy, composed by 12 effects with parallel-feed configuration and equipped with a medium-pressure steam vapour ejector.

This work describes the performance of the first RED prototype plant fed with real brackish water and saltworks brine

Reverse electrodialysis (RED) is a promising technology for electric power generation by the chemical potential difference of two salt solutions within a stack equipped by selective ionexchange membranes (salinity gradient energy). Mechanical energy is required for pumping the feed solutions, which can reduce dramatically the net power output. In this work Computational Fluid Dynamics (CFD) simulations of spacer-filled channels for RED were carried out in parallel with an experimental campaign focused on the collection of data for model validation.

Different spacer features and operating conditions were investigated in order to identify a good compromise between concentration polarization and pumping power reductions.

La presente invenzione riguarda un reattore e un procedimento per eseguire processi di cristallizzazione reattiva con elevata selettività, consentendo di evitare la miscelazione diretta tra le due soluzioni contenenti i reagenti della reazione e di minimizzare l’effetto di reazioni secondarie indesiderate. Per brevità, nel testo seguente tale reattore e procedimento verrà indicato con l’acronimo CrIEM (Crystalliser with Ion Exchange Membrane).

Power savings is a problem of crucial importance nowadays. In process industry, suspension of solid particles into liquids is usually obtained by employing stirred tanks, which often are very power demanding. Notwithstanding tanks provided with baffles are traditionally adopted for this task, recent studies have shown that power reductions can be obtained in top-covered unbaffled vessels. In the present work experiments were carried out in a top-covered unbaffled vessel with a diameter T=0.19m and filled with distilled water and silica particles. Two different turbines were tested: a standard six-bladed Rushton Turbine (RT) and a 45° four bladed Pitched Blade Turbine (PBT). For the case of the PBT both the up-pumping (PBT-Up) and the down- pumping (PBT-Down) operation mode were tested. Two different impeller sizes D (T/3 and T/2) and clearances C (T/3 and T/10) were investigated. The effects of particle size and concentration were also assessed. Investigations concern the assessment of the minimum impeller speed for complete suspension (Njs) along with the measurement of the relevant power consumption (Pjs) aiming at identifying the most efficient tank-turbine configuration among those investigated here. Results were also compared with corresponding ones pertaining to baffled tanks (obtained via correlations available in the literature). Results have shown that the RT with D=T/3 and C=T/3 and the PBT-Up with D=T/2 and C=T/10 appear to be the most convenient (least power demanding) options. Finally, a significant power saving with respect to the most efficient baffled configurations was observed thus confirming the convenience of operating solid-liquid suspensions in an unbaffled system for all those processes where the mixing time is not a limiting factor.

Cultivation of microorganisms, plants or animal cells requires liquid agitation in order to ensure oxygen and nutrient transfer and to maintain cell suspension. Many studies on animal cell damage due to mechanical agitation and sparging aeration have shown that mechanical damage of freely suspended animal cells is in most cases associated with bursting bubbles at the air–liquid interface (Barrett et al., 2010). Gas bubbles are usually generated by direct air sparging aimed at supplying oxygen to the culture medium. Mechanical agitation may also introduce gas bubbles in the culture medium via vortexing entrainment from the free surface. In this work oxygen transfer performance of an unbaffled stirred bioreactor, with various aspect ratios, is presented in view of its use as a biochemical reactor for animal cell growth. In practice oxygen mass transfer occurs through the (more or less deep) free surface vortex which takes place when agitation is started in unbaffled vessels. If this vortex is not allowed to reach impeller blades, bubble formation and subsequent bursting at the free-surface is avoided. Experimental results show that this kind of bioreactor can provide sufficient oxygen mass transfer for animal cell growth, so resulting in a viable alternative to the more common sparged reactors. The mass- transfer performance observed with the different aspect ratio configurations is also presented and discussed.

Reverse Electrodialysis (SGP-RE or RED) process has been widely accepted as a viable and promising technology to produce electric energy from salinity difference (i.e salinity gradient power - e.g. using river water/seawater, or seawater and concentrated brines). Recent R&D efforts demonstrated how an appropriate design of the SGP-RE unit and a suitable selection of process conditions may crucially enhance the process performance. With this regard, a process simulator was developed and validated with experimental data collected on a lab-scale unit, providing a new modelling tool for process optimisation. In this work, performed within the REAPower project (www.reapower.eu), the process simulator previously proposed by the authors has been adopted for a wide sensitivity analysis of the SGP-RE process. The aim of this analysis is to investigate the influence of the most relevant variables (i.e. solution properties, stack geometry) on the overall process performance. In particular, the use of different salt concentration for feed streams, as well as flow rates and membrane sizes have been taken into account as optimisation variables. Different stack sizes were investigated, starting from a 10x10 cm2 lab-stack, up to a 44x100 cm2 large prototype unit. Finally, different scenarios are proposed for a prototype-scale plant, providing useful indications for the technology scale-up towards 1 kW of power production. These model predictions will be eventually used to address the economic feasibility of the SGP-RE technology for large scale applications.

In the present work, a recently presented experimental technique, based on the use of thermochromic liquid crystals (TLCs) and digital image processing, has been employed in order to measure the temperature and local heat transfer coefficient distribution on the membrane surface in a MD spacer-filler channel

Reverse electrodialysis (RE) is a promising technology for electric power generation by converting the chemical potential difference of a salinity gradient, within a stack equipped by selective ion-exchange membranes. Concentration polarization phenomena and pressure drop affect strongly the power output obtainable; therefore the channel geometry is a fundamental operating parameter for the optimization of the system. In this work, Computational Fluid Dynamic simulations were performed to predict fluid flow and mass transfer in spacer-filled channels for RE applications. A parametric analysis for different spacer geometries was carried out; in particular, woven and non woven spacers were simulated, with different pitch to height ratios, at various Reynolds numbers typical of RE channels, and with two different orientation. From the rigorous Stefan–Maxwell equation along with the assumptions of binary electrolyte and local electroneutrality, the transport equation was obtained. Periodic boundary conditions were adopted to simulate a fully developed flow. Simulation results show how the parameters investigated influence pressure drop and concentration polarization, thus suggesting the features that a spacer should have in order to obtain high process performance.

Reverse electrodialysis (RE) is a promising technology for electric power generation from controlled mixing of two differently concentrated salt solutions, where ion-exchange membranes are adopted for the generation of ionic currents within the system. Channel geometry strongly influences fluid flow and thus crucial phenomena such as pressure drop and concentration polarization. Profiled membranes are an alternative to the more commonly adopted net spacers and offer a number of advantages: avoiding the use of non-conductive and relatively expensive materials, reducing hydraulic losses and increasing the active membrane area. In this work, Computational Fluid Dynamic simulations were performed to predict the fluid flow and mass transfer behaviour in channels with profiled membranes for RE applications. In particular, channels equipped with pillars were simulated. The influence of channel geometry on fluid flow and concentration polarization was assessed by means of a parametric analysis for different profile geometries. The unit cell approach along with periodic boundary conditions was adopted to simulate fully developed boundary conditions. Transport equations, valid also for concentrated solutions, were obtained from the rigorous Stefan–Maxwell equation along with the assumptions of binary electrolyte and local electroneutrality. Simulation results show that, in the geometries investigated here, the pumping power consumption is much lower than in a conventional net spacer and very close to that of the empty channel, while calm zones are generated by the profiles, which may accentuate polarization phenomena.

The present work focuses on the development of a novel computational code able to predict with a reasonable level of accuracy the bubble behavior in gas fluidized beds with minimum computational demands. The code simulates the bubble chaotic rise motion and coalescence along bed height via simple lagrangian tracking of bubbles. An original empirical model for the assessment of bubble-bubble interactions is developed. The code is used to simulate a lab-scale unit in bubbling and slugging mode. On this basis, fast simulations are performed to successfully predict bubble population and fluxes within the bed. The main aim of this code is to be embedded within CAPE codes for the process simulation. The model adopted by the code is also well suited for multi-scale modeling approach since physical parameters can be obtained from both experimental data or CFD simulation. Preliminary results of the simulations, in terms of distributions for bubble size and number as well as local hold up values, are compared with relevant experimental data.

Solid-liquid mixing within tanks agitated by stirrers can be easily encountered in many industrial processes. It is common to find an industrial tank operating at an impeller speed N lower than the minimum agitation speed for the suspension of solid particles: under such conditions the distribution of solid-particles is very far from being homogeneous and very significant concentration gradients exist. The present work evaluates the capability of a Computational Fluid Dynamics (CFD) model to reliably predict the particle distribution throughout the tank under either partial or complete suspension conditions. A flat bottomed baffled tank stirred by a Rushton turbine was investigated. Both transient and steady state RANS simulations of the stirred tank were performed with the commercial code CFX4.4. The Eulerian-Eulerian Multi Fluid Model along with the k-ε turbulence model was adopted. Either the Sliding Grid or the Multiple Reference Frame technique was employed to simulate the impeller to baffle relative rotation. Inter-phase momentum exchange terms were approximated only by the inter-phase drag forces. Literature experimental data were used for the model validation. Results show that the model along with the Sliding Grid technique can reliably predict the experimental particle distribution at all investigated impeller speeds. Radial gradients of solids concentration, usually neglected in the literature, where found to be significant in the presence of unsuspended solid particles (partial suspension conditions).

In this work, carried out within the EU-FP7 funded REAPower project, CFD simulations were carried out in order to study the fluid flow behaviour and mass transport phenomena within spacer-filled channels.

In the presente work, CFD simulations were carried out in order to assess the effects of different parameters on the global process efficiency, such as the choice of spacer material and morphology, and the optimisation of feed and blowdown distribution systems

Apparato di sintesi su letto catalitico e di separazione dei prodotti di sintesi comprendenti una fase gassosa e due fasi liquide, una fase liquida più pesante e l’altra fase liquida più leggera, l’apparato comprendente - un modulo di sintesi (M1) comprendente un primo tubo (1) provvisto ad una prima estremità di un’apertura e chiuso ad una seconda estremità da una griglia (7), il primo tubo (1) essendo atto a contenere al suo interno un letto catalitico (6); - ed un modulo di separazione (M2) per separare le due fasi liquide e la fase gassosa provenienti dal modulo di sintesi (M1), comprendente un secondo tubo (1’) disposto adiacente alla seconda estremità del primo tubo (1), comunicante con esso ad una sua prima estremità, ed avente ad una sua seconda estremità un elemento di chiusura (13) provvisto di un foro passante.

Multi Stage Flash desalination technology has been a leading technology in the desalination market for the last four decades. However as a result of the continuous increase of costs for the special materials required for the tube bundles the share of MSF technology in the market is nowadays steadily shrinking. Aim of the present work is to present a novel configuration for the MSF process. In the proposed arrangement evaporation occurs in a multi stage vertical column filled with packing material to enhance the achievement of flashing equilibrium in each stage, while condensation occurs in a second column through direct mixing with a colder water stream. Thermal integration for the recovery of condensation latent heat is performed by an external plate-and-frame heat exchanger, which reduces dramatically the quantity of special materials required at the same time significantly enhancing the heat transfer. A preliminary analysis of feasibility and potentials of such process is presented.

Mixing of solid particles into liquids in mechanically agitated vessels is a topic of primary importance for several industrial applications. A great deal of research efforts has been devoted so far to the assessment of the minimum impeller speed (Njs) able to guarantee that all particles are suspended. Conversely, only little attention has been paid to the evaluation of the amount of solid particles that are suspended at impeller speeds N lower than Njs, despite the fact that in a number of industrial applications agitation speeds smaller than Njs are actually adopted [1,2]. The present work deals with dense solid-liquid partial suspensions in baffled stirred tanks and particularly focuses on the prediction of the amount of suspended particles at a number of angular velocities by means of Computational Fluid Dynamics. An Eulerian-Eulerian Multi Fluid Model coupled with a standard k-epsilon turbulence model is adopted for CFD simulations. Both Sliding Grid and Multiple Reference Frame approaches are employed to simulate the impeller-tank relative rotation. The computational model is validated by comparison with purposely collected experimental data. 1.Oldshue, J. Y., (1983). Fluid Mixing Technology, Chapter 5, McGraw-Hill, New York, NY. 2.Rieger, F., Ditl, P., Havelkova, O., (1988). Suspension of solid particles–concentration profiles and particle layer on the vessel bottom. Proceedings of the 6th European Conference on Mixing, Pavia, Italy, 24-26 May, 251-258.

This work concerns a new experimental technique based on Digital Image Analysis aimed at the measurement of the mixing behaviour of the granular phase in a 2D fluidized bed. In particular, the preliminary results obtained about the mixing pattern of a bi-disperse 2D gas fluidized bed are reported. Two different kind of particles were fluidized having the same density but different size. The technique is based on suitable colour-field decomposition of the fluidized bed, in which particles of different colours are employed. The technique here proposed can effectively measure the concentration field in the whole bed during operation, thus obtaining data that can be reliably used for CFD simulation validation. Moreover, it is possible to follow the mixing and segregation dynamics of powders in the fluidized bed. Notably, the technique here developed can be used for both gas-solid or liquid-solid fluidized beds.

Desalination technologies nowadays is a very interesting and emerging alternative to conventional water sources; their high energy consumption, however, generates some problems in adopting them, especially in remote areas where electric grid is not available and fuel transportation is not always sustainable. In this paper a short overview of possible couplings between the membrane distillation technology for desalination and the use of sustainable thermal energy sources is presented. Two case studies of ongoing research projects at Università di Palermo are also presented.

The availability of experimental information on solid distribution inside stirred tanks is a topic of great importance in several industrial applications. The measurement of solid particle distribution in turbulent multiphase flow is not simple and the development of suitable measurement techniques is still in progress. In this work a novel non-intrusive technique for measuring particle concentration fields in solid-liquid systems is employed. The technique makes use of a laser sheet, a high sensitivity digital camera for image acquisition and a Matlab procedure for post-processing the acquired images. Experimental data are here obtained for the case of an unbaffled stirred tank. Stable toroidal attractors for particles are observed under given circumstances. Their existence, consistency and extension depends on particle type, fluid properties, tank geometry and impeller velocity.

In the field of gas–solid fluidization, bubbles, and all features regarding them, have a very great importance, as they significantly affect the process performance. Numerous experimental studies on bubbles, and their formation, evolution, and properties, have been performed in the past. These investigations appear particularly difficult, due to the nature of these systems, since the gas phase is distributed in both the bubble and the emulsion phase. Several experimental approaches have been developed to tackle this study. Among these, the Digital Image Analysis Technique purposely developed in Part I of the present work, based on the use of a video camera for monitoring the phenomenon coupled with image analysis has been found viable and effective. Moreover, the bubbles behaviour and characteristics have been described by means of a variety of mathematical models. In recent years, in particular, computational fluid dynamics (CFD) tools have been found to be very effective in providing a powerful framework through which these models can be implemented and numerically solved. This paper combines both experimental and computational studies, presenting the comparison, performed by DIAT, between experimental data and relevant CFD simulations. In particular, simulations have been performed by means of the ANSYS-CFX code. The comparison comprises the following quantities: bed expansion, bubble hold-up, size evolution, distribution, density, aspect ratio, and bubble velocimetry data.

Unbaffled stirred tanks are seldom employed in the process industry as they are considered poorer mixers than baffled tanks. However, they might provide significant advantages in a wide range of applications like crystallization processes as well as for food and pharmaceutical industries, where the presence of baffles is often undesirable. In the present work solid-liquid suspension in an unbaffled stirred tank was investigated. A novel experimental method (steady cone radius method) was devised to ease the evaluation of the minimum impeller speed for complete particle suspension (Njs). Experiments encompassed a quite wide range of particle sizes, densities and solids concentration. The Njs values obtained were compared with the relevant values pertaining to baffled vessels, estimated by means of the well known Zwietering’s correlation. Dependence of Njs on particle density and concentration was found to be similar for both types of tank. Conversely, a negligible influence of particle diameter on Njs was observed in the unbaffled tank, thus marking a difference from baffled tanks with important application implications. Finally the Njs values obtained in the unbaffled vessel are generally smaller than the corresponding Njs in baffled tanks. This finding, in conjunction with the much smaller Power Numbers exhibited by the former, suggests that the power consumption required to achieve complete suspension in unbaffled tanks may be much smaller than in baffled systems.

The availability of experimental information on solid distribution inside stirred tanks is a topic of great importance in several industrial applications. The measurement of solid particle distribution in turbulent multiphase flow is not simple and the development of suitable measurement techniques is still in progress. In this work a novel non-invasive technique for measuring particle concentration fields in solid-liquid systems is presented and employed. The technique makes use of a laser sheet, a high sensitivity digital camera for image acquisition and a Matlab procedure for post-processing the acquired images. Experimental data are here obtained for the case of an unbaffled stirred tank provided with cover. Stable toroidal attractors for particles are observed under given circumstances. Their existence, consistency and extension dependence on particle inertia properties and impeller angular velocity is investigated and discussed.

Bubble characteristics are very important in the design of fluidized beds because they govern hydrodynamics and efficiency of the operation for which the bed is used. In this work, a digital image analysis technique has been developed to study the fluidization dynamics of a lab-scale two-dimensional bubbling bed. Digital image analysis may supply a great quantity of information; it is non-intrusive, capable of securing several properties simultaneously and cost effective. The image analysis method here developed allows for the simultaneous measurements of various significant bubble properties, i.e. bubble size and bubble velocity distributions, bed height and bubble-phase hold-up, by means of a purposely in-house developed software. Present results were compared with relevant literature correlations and resulted in sound agreement, thus confirming the large potential of the technique here developed.

In recent years the use of Computational Fluid Dynamics (CFD) is significantly increasing to simulate multi-phase flows. It is invariably emphasized that a necessary step towards the development of reliable fully predictive CFD models is an extensive experimental validation of the simulation results. This work in particular focuses on the CFD simulation of a lab-scale 2D fluidized bed and the relevant experiments, in order to validate the prediction capability of the used codes and models. It must be emphasized that both experimental and computational quantitative data have been obtained by means of an original Digital Image Analysis Technique, that allows coherent comparison of computational and experimental data. Due to the great importance of bubbles dynamic in affecting the fluidization quality, this work analyzes the capability of the CFD simulations in predicting the fluctuating behaviour of fluidized beds, by means of frequency analysis of bubbles related phenomena.