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This work analyses the correlation between external heat transfer and fluid dynamic field near a surface immersed in a bubbling fluidised bed through a simplified model and detailed DEM-CFD simulations. The study is based on experimental results on surface-to-bed heat transfer between a fluidised bed at bubbling and slugging regime and two heat transfer probes with spherical and cylindrical shape. The model estimations and the DEM-CFD simulations have been compared in terms of estimated values of averaged surface void fraction εw. The two approaches give similar results for the case of the sphere while the value of εw for the cylinder deduced by numerical simulations appears to be underestimated.

The paper presents experimetnal findings on an innovative system aimed to remove ultrafine particles from gases. The system is based on coupling a particle enlargement process with a three-phase bubble column. Calibrated polystyrene nanoparticles of about 200 nm were tested and were enlarged in a growth-tube operated at different temepartures to obtain different super-saturation levels. The experimental results showed that the aerosol cumulative distribution functions shifted towards larger diameters with the increasing of supersaturation; the total particle removal efficiency in the three-phase bubble column increased with the supersaturation reaching values of 99 %.

The absorption of SO2 in electrified water sprays, either when the polluted gas is treated as is or when the gas is exposed to a corona source to ionize the SO2 was evaluated. An electrified spray with a charge-to-mass ratio of 50 ΜC/kg enabled the absorption rate of droplets to double, regardless of their polarities. Corona charging gave rise to an increase in the SO2 depletion rate over the scrubber wall, while negligible effects appeared on the actual droplets absorption rate. These findings suggested that faster absorption rates mostly, though not uniquely, depend on the modifications on the morphological and interfacial properties of the sprayed droplets induced by the free electric charge imposed on their surface. Conversely, the absorption rates were negligibly affected by the electrical interactions between droplets (either charged or uncharged) and the SO2 ions/radicals originating from the corona source.

Several studies indicate that short-sea shipping is an important source of air pollution for coastal areas and port cities. This paper reports results of a non-reactive particles dispersion model and a new set of experiments implemented for the Channel of Procida (Italy), an area with a high signal-to-noise ratio, due to intense marine traffic and low background pollution. The model successfully predicts particle number concentrations but underestimates PM2.5 data. Model and experiments show that thanks to the EU policies on marine fuels, the Channel of Procida already has good air quality levels. Besides, the paper demonstrates that fostering the use of LNG or methanol or the application of an exhaust-gas-cleaning-system may allow reducing particles emissions well above 90%. The reliability of control strategies and the benefits for the population suggest that the introduction of regulations on particles emissions for ships can be a realistic option for the future environmental policy agenda.

The work deals with the adsorption of cadmium and zinc on coal combustion ash (CCA) sorbents, in both single-compound and binary systems. Three sorbents were tested; one is CCA as received, the other two derived from the gasification of raw CCA carried out with either steam (SG sample) or carbon dioxide (DG sample). Experimental adsorption runs showed a significantly higher adsorption capacity of zinc with respect to cadmium, for all the investigated sorbents. This was ascribed to a higher affinity of sorbent active sites towards Zn(II) and, secondarily, to the smaller dimension of zinc cations (Zn2+), which resulted to be less affected by steric hindrance. Moreover, for both the analytes, a ranking DG > SG > CCA of adsorption capacity can be recognized. This is likely due to the increase in inorganic fraction of SG and DG sorbent with respect to CCA, due to the gasification treatments. Moreover, for DG sorbent, further improvement of the performances could be ascribed to an increase in the concentration of oxidized surface functional groups, which are considered the preeminent active sites for zinc and cadmium adsorption on the investigated sorbents. Binary adsorption data showed the same ranking among sorbents retrieved in single-compound tests and a higher zinc adsorption capacity.

The paper shows experimental findings aimed to prove the effectiveness of a concept design for fine and ultrafine particle capture called condensational growth assisted bubble column. Experiments were carried out with a gas at ambient temperature and pressure polluted with calibrated polystyrene nanoparticles (mean numeric diameter 113 nm, standard deviation 120 nm). The laboratory scale equipment included the sequence of a growth tube and a bubble column. In the growth tube, the heterogeneous condensation of water vapour took place over the particles, producing a liquid-solid aerosol of size larger than the original particles. Experiments showed that the condensational growth pre-treatment improved the bubble column removal efficiency from nearly 25 % up to 90 %. The growth tube also contributed to particle capture so that the overall system reached particle removal efficiency above 95 %. The particle removal efficiency of the entire unit was higher than the sum of the single growth tube and bubble column contributions, suggesting the occurrence of favourable synergic effect between them.

The production of secondary precious and rare-earth metals is a key topic for sustainable development, due,to the increasing demand and the lowering of natural resources. Palladium is one of the most largely used noble metals, and there is an increasing interest toward its recovery from waste materials. Processes for secondary palladium production often include refinery processes in which the metal must be recovered from an acid leachate. Adsorption and ion-exchange are among the most reliable refinery methods. In the past years, several interesting studies deeply investigated the palladium capture capacity of ionic exchangers or functionalized biomasses. Thanks, to its mechanical properties, market size, industrial experience in process design and relatively low cost, the simple, non-impregnated, activated carbon may occupy a niche market in the production of secondary palladium. This paper reports experimental evidences on the capture of palladium over two commercial activated carbons, one derived from bituminous coal and one from coconut shell. Model solutions of palladium in both HNO3 and HCl were adopted and pH, temperature and salinity (in NaNO3 and NaCl) were varied. The experiments revealed that palladium adsorption in HC1 is about ten times higher than in HNO3. Moreover, palladium adsorption was almost insensitive to pH and salinity variation, while it reduced with temperature. A comparison with the pertinent literature was based on the values of the adsorption capacity in two reference liquid concentration, one referred to a high leachate concentration, 15 mg L-1, and one referred to a tentative final concentration of 1 mg L-1 .The adsorption capacities of the activated carbons in the two cases were higher than 60% and 76% of the compared materials. The experimental results suggest that palladium capture took place over the protonated basal plane of the carbon thanks to a network of adsorption and redox reactions, which led to the formation of elemental palladium over the carbon surface. Besides, palladium micro-precipitation also took place at pH between 3 and 4.5, further increasing the overall uptake capacity on the sorbent. (C) 2016 Elsevier B.V. All rights reserved.

The photocatalytic reduction of nitrate to nitrogen and the simultaneous production of hydrogen was investigated over copper loaded titania (P25) nanoparticles using glycerol as sacrificial agent and UV-A/Vis radiation. The experiments demonstrated that total nitrogen (i.e., nitrate, nitrite, and ammonia) removal efficiencies over 93% were achieved for initial nitrate concentrations up to 150 mg/I. A parallel hydrogen production up to 14 mu M was recorded. Hydrogen generation was affected by nitrate reduction. The reaction rates were dependent on pH and both glycerol and nitrate starting concentrations in the mixture. However, a linear model can be used to describe the process for low concentration of nitrate and constant pH. The system showed a remarkable photoefficiency in decontamination of nitrate-containing solutions and concomitant hydrogen evolution. This study lays the foundation for the future development of numerical models able to predict the chemical behavior of simultaneous proton and nitrate reduction over solar photocatalytic reforming of organics. (C) 2016 Elsevier B.V. All rights reserved.

Flue Gas Desulphurization (FGD) is a key topic for most of combustion fossil fuel plants and industrial applications. Wet processes are usually preferred when the removal efficiency required to comply with environmental regulation exceed 90 %, but their flexibility makes them useful also for lower performance requirements. Recently, seawater has been considered as a viable absorbent for FGD processes in coastal and naval applications, when SO2 concentration is below 1000 ppmv. This liquid absorbs SO2 mostly thanks to its natural alkalinity (on average 2.4 mmol/L) and, of course, is also largely available. The main costs of seawater FGD (SW-FGD) plants are related to the pumps needed to supply the required amount of liquid and the cost of wash water restoration before discharge. Corrosion related to the presence of acidic seawater is also a major issue of these units. While thermodynamic limitations cannot be overcome, process design can be optimized to improve mass transfer rates and reduce seawater requirements while keeping a suitable absorber size. In this work, we report the experimental findings achieved by our group on process design and optimization of SW-FGD units. Two different kinds of SW-FGD units were tested and compared: a spray column and a packed column with structured packing.

This paper explores the effects of electrification of water sprays on the absorption of sulphur dioxide from exhaust gases. Electrification is associated with an appreciable improvement of sulphur dioxide absorption rate with low supplementary costs and candidates to be a valuable innovation for spray tower absorbers. Similar phenomena occur during thunderstorms, when scavenging of gases and aerosol are enhanced by the electric charge of raindrops. This paper aims to describe the effects of electrification on SO2 absorption on the bases of experimental and theoretical analyses. The experiments involve absorption tests in lab-and pilot scale facilities, while theoretical modelling to assess the chemical and physical properties of charged droplets, their hydrodynamics and their mass transfer rates are presented. Water electrification is accompanied by a number of chemical-physics and morphological modifications of the sprayed droplets that modify the conventional absorption rate of soluble gases. The experimental and theoretical evidences indicate the need to analyse the electrified absorption within a new and integrated theoretical framework that we define chemi-electro-hydrodynamics (CEHD).

This paper investigates the application of K 2 CO 3 supported onto porous alumina, as sorbent for selective CO 2 capture in marine applications. Alumina-functionalized sorbents were prepared by incipient wetness impregnation achieving K 2 CO 3 loadings from 3.6 to 14.1% wt. Carbonation tests were performed in a fixed-bed column at temperatures between 60 and 105 °C, as those typically occurring at the outlet of a scrubber and/or a waste heat recovery unit, with a model diesel engine exhaust (5% vol. CO 2 , 5% vol. H 2 O, balance N 2 ). According to the carbonate loading, the sorbents may reach conversion degrees of carbonate up to 90% and overall capture capacity up to 0.66 mol kg −1 sorbent. Experimental data showed higher conversion degree and capture capacity compared with unsupported K 2 CO 3 , which is affected by significant intraparticle diffusion limitations. Steam regeneration tests performed in a fixed-bed column on the sorbent with 3.6% wt K 2 CO 3 loading revealed that a temperature of 120 °C assures almost complete recovery of captured CO 2 while preserving the sorbent carbonation degree for 10 consecutive carbonation/regeneration cycles. The preliminary design of a temperature swing carbonation/regeneration unit for on-board ship installation was performed for the reference case study of a passenger ship equipped with a 4.35 MW marine engine fueled with marine gas oil and with a commercial seawater scrubber for SO 2 removal. The proposed unit appeared able to cut up to 30% carbon dioxide emission by using the sorbent containing 3.6% wt K 2 CO 3 and operating the carbonation and regeneration stage at 60 and 120 °C, respectively.

This paper aims to evaluate how condensational growth may be used to improve the performances of a Venturi scrubber in removing soot particles, which are among the most relevant air pollutants emitted in industrial and power plants exhaust gases. Former studies on this system, called Condensational Growth assisted Venturi scrubbers (CGVS), suggested that the most relevant step to address their efficiency is the assessment of the amount of water that condense on the soot particles, which determines the actual aerosol size distribution entering the Venturi. Unfortunately, a definite physical mathematical model to predict the actual condensational growth of an ensemble of non-spherical particles is not yet available and experimental investigation is better suited to assess this point. This study reports experimental data on the size distribution achieved by exposing model soot particles to a water supersaturated gas for different residence times. The obtained size distributions are used to estimate the efficiency of a Venturi scrubber in removing the water-soot aerosols, allowing a comparison with the removal of parent soot particles. The experiments were carried out at lab scale by using a laminar-flow growth tube, a simple device to perform a controlled condensational growth. The experiments indicated that, even for a hydrophobic material as soot, condensational growth is effective even at supersaturation levels as low as 1.02. Liquid-solid aerosols from nearly 2 to >3 times larger than the parent particles are produced with a supersaturation level lower than 1.15. Finally, the analysis of experimental data indicated that the fraction of particles subjected to condensational growth is relevant. Indeed, calling as ψ the fraction of particles that become larger than the 98% percentile of the original particle size distribution, we found that ψ can be as high as 78%. The analysis of data indicated that an appreciable linear correlation exits among ψ and the 95th percentile of the supersaturation level, S95, while not being dependent on the exposure time. The experimental evidences suggest that the adsorption of water molecules over the soot surface overcome the effects of hydrophobicity and of line tension effects, favouring condensation of water over the soot surface and leading to a higher nucleation rate even at low supersaturation. Application of the Venturi scrubber model to the water-soot aerosol leaving the growth tube indicate that the CGVS may remove particles with an efficiency far higher than that achieved by the stand alone Venturi. For a given Venturi's throat length and velocity and a given liquid-to-gas ratio, the CGVS efficiency depends almost linearly on ψ and, in turns on S95. Experimental and model results suggested that the CGVS can be a valuable and effective device to capture soot particles and that condensational growth can be used as a retrofit method for existing units. © 2018 Elsevier B.V.

In this work, the results of equilibrium and dynamic adsorption tests of hexavalent chromium, Cr (VI), on activated carbon are presented. Adsorption isotherms were determined at different levels of pH and temperature. Dynamic tests were carried out in terms of breakthrough curves of lab-scale fixed bed column at different pH, inlet concentration and flow rate. Both the adsorption isotherms and the breakthrough curves showed non-linear and unconventional trends. The experimental results revealed that chromium speciation played a key role in the adsorption process, also for the occurrence of Cr(VI)-to-Cr(III) reduction reactions. Equilibrium tests were interpreted in light of a multi-component Langmuir model supported by ion speciation analysis. For the interpretation of the adsorption dynamic tests, a mass transfer model was proposed.Dynamic tests at pH 11 were well described considering the external mass transfer as the rate controlling step. Differently, for dynamic tests at pH 6 the same model provided a satisfying description of the experimental breakthrough curves only until a sorbent coverage around 1.6mgg-1. Above this level, a marked reduction of the breakthrough curve slope was observed in response to a transition to an inter-particle adsorption mechanism. © 2014 Elsevier B.V.

This study reports experimental results on the primary jet breakup parameters of three hollow cone hydraulic spray nozzles electrified by induction. While former evidence indicated that the properties of sprayed droplets are scarcely affected by induction charging, we found that an increase in charging potential from 0 kV to −10 kV led to a reduction of breakup length and an increase of spray angle. For charging potential from −10 kV and −12 kV both the parameters reached asymptotic levels. As for electrosprays, we argue that jet breakup reduction modifications depend on the establishment of electrical stresses over the water sheet, while spray angle enlargements depend on the repulsion forces caused by induced charges. In most of the cases, these modifications are not sufficient to change the secondary atomization regime, but they severely affect the charging level of sprayed droplets.

[object OThe photocatalytic removal of nitrate with simultaneous hydrogen generation was demonstrated using zero-valent nano-copper-modified titania (P25) as photocatalyst in the presence of UV-A-Vis radiation. Glycerol, a by-product in biodiesel production, was chosen as a hole scavenger. Under the adopted experimental conditions, a nitrate removal efficiency up to 100% and a simultaneous hydrogen production up to 14 ?mol/L of H2 were achieved (catalyst load = 150 mg/L, initial concentration of nitrate = 50 mg/L, initial concentration of glycerol = 0.8 mol/L). The reaction rates were independent of the starting glycerol concentration. This process allows accomplishing nitrate removal, with the additional benefit of producing hydrogen under artificial UV-A radiation. A kinetic model was also developed and it may represent a benchmark for a detailed understanding of the process kinetics. A set of acute and chronic bioassays (Vibrio fischeri, Raphidocelis subcapitata, and Daphnia magna) was performed to evaluate the potential ecotoxicity of the nitrate/by-product mixture formed during the photocatalytic process. The ecotoxicological assessment indicated an ecotoxic effect of oxidation intermediates and by-products produced during the process. © 2017, Springer-Verlag Berlin Heidelberg.bject]

Hydrophilic carbonaceous nanoparticles (HNPs) of uniform sizes with a good degree of dispersion in water were produced from a commercial carbon black by nitric acid treatment. The surface treatment, performed at different reaction times, generates a variable number of oxygen functional groups, mainly carboxylic, which enhance the nanoparticles hydrophilicity and heavy metal adsorption capability. The HNPs were characterized by a number of analytical techniques, including FTIR spectroscopy, thermal and elemental analysis, N2 adsorption, dynamic light scattering, and zeta-potential measurements. The acid–base properties of the functional groups on the HNPs surface were also investigated by coulometric–potentiometric titrations. Cadmium adsorption tests were carried out in stirred reactors containing colloidal aqueous suspensions of HNPs and HNPs supported over silica. The effects of several parameters, such as the cadmium concentration, the temperature, and the solution pH, were studied. Sorbents showed an appreciable cadmium adsorption capability at different temperatures and in a wide range of pH values comparable or superior to several carbon-based sorbents, indicating a feasible use in commercial units.

This work aims to the analysis of arsenic desorption from an exhaust activated carbon used for the purification of a natural water. This last was used to mimic the properties of common groundwater or drinking water. Different low-cost and harmless eluting solutions were considered, including distilled water, natural water, saline (NaCl, CaCl2 and NaNO3) and basic (NaOH) solutions. Experimental results showed that, for 1 g of activated carbon with arsenic loading close to the maximum value available for the model natural water (omega approximate to 0.1 mg/g), it is possible to recover more than 80% of the arsenic using 20 ml of 0.1 M sodium chloride solution. A temperature variation within 20 and 40 degrees C has scarce effect on desorption efficiency. A comparison between desorption data and adsorption isotherms data suggests that arsenic adsorption is actually a reversible process. Therefore, it is virtually possible to increase arsenic recovery efficiency close to 100% by increasing the NaCl concentration or the volume of the desorption solution, but a preliminary cost benefit analysis lead to consider a NaCl 0.1 M solution as an optimal solution for practical application.

This paper describes lab scale experiments that were carried out to determine the scavenging rate of submicron particles in the presence of charged droplets, which helps to study the mechanisms involved in wet electrostatic scrubbing process. The main aim of this study is the need to decouple the effects of particles–droplets interactions from the specific features of the electro-hydrodynamics of a charged spray. To this end, a novel experimental methodology was developed to carry out tests with an electrospray operating in dripping mode to produce a train of uniformly sized and charged droplets. Experiments were performed either with charged or uncharged particles in order to understand the differences between wet electrostatic scrubbing in the presence of electric forces, when both droplets and particles are charged, or in the presence of image charge forces only, when particles are uncharged. The obtained results demonstrate that the particle image charge effect does not lead to appreciable particle abatement, while Coulomb interactions become the dominant particle scavenging mechanism when particles are charged. In this case, the scavenging rate can be described by a first order equation in particles concentration and the experimental results are consistent with theoretical predictions based on the classical model of atmospheric scavenging.

New regulations regarding the PM1 emission by power plants and transport vehicles require novel technical solutions for the abatement of particulate matter emission in submicron size range. Particles of this size are difficult to remove by conventional methods, and therefore various variants of wet electrostatic scrubbers have been developed. In such devices, the electrostatic forces between charged particles and collectors (water droplets) are used to permanently remove them from the gas. The paper focuses on the state-of-the-art of wet electrostatic scrubbing technique used for the removal of submicron particulate matter from exhaust gases with particular emphasis upon marine Diesel engines.

Heat and mass transfer coefficients between bubbling fluidised beds and immersed surfaces are analysed in light of recent findings that clarify the properties of the emulsion phase in proximity of immersed surfaces. The correlation between heat and mass transfer in fluidised beds is not straightforward since the two phenomena obey to different transport mechanisms, so that the classical Chilton–Colburn analogy is not valid any longer. Therefore, the link between the two phenomena can be achieved only through a deeper understanding of the fluid dynamic and morphological characteristics of the granular flow in proximity of the exchange surface. In this paper, results available in the pertinent literature are critically compared and used to provide a simple methodology to correlate the average and local heat and mass transfer coefficient with the fluid dynamic field for the case of a horizontal cylinder immersed in a bubbling fluidised bed.

In this study, we investigated the induction charging of water sprays and the effect of electric field on the breakup mechanism of liquid sprays. Two different kind of hollow cone hydraulic spray nozzles were used. Our investigation aimed to estimate the Droplet Charge to Mass Ratio (D-CMR) and the dependence of breakup length on electric potential. The experiments revealed that the D-CMR increased with the potential until to a maximum, then started to decrease. At the same time, the breakup length decreased more than 0.5 cm compared to the uncharged value, suggesting that the electric field actually influenced the jet break-up dynamics. For V

This paper proposes a process for reducing the content of copper and zinc in polluted soils and a combined photocatalytic-physical process for the treatment of the soil washing effluents. For this purpose, real soil samples were taken from the "Land of Fires", a region in Southern Italy which is known for its high incidence of cancer mortality. Ethylenediamine-N,N'-disuccinic acid (EDDS) was used to extract the heavy metals from the contaminated soil. The soil washing effluents were treated through a sequence of photocatalytic and adsorption processes to lower the concentration values of metals (Cu, Zn, Fe and Mn) below the limits of national legislation for discharge in municipal sewers and to remove the EDDS from the soil washing solutions. Ecotoxicological tests, using different living organisms (Daphnia magna, Vibrio fischeri, Pseudokirchneriella subcapitata and Lepidium sativum), were performed on the soil washing effluents before and after the treatments to assess the effects of the proposed combined process on the ecotoxicity of the soil washing solutions.

This paper reports preliminary results on the absorption of SO2 from water charged droplets, produced by an electrospray operated in dripping mode. Our results show that the water charging allows a ˜50% increase of the SO2 absorption rate. Since the SO2 mass transfer coefficient depends mainly on the liquid-side mass transfer coefficient, we envisage that the increase of SO2 absorption rate is ascribable to the occurrence of droplet deformation and oscillation, driven by the reduction of surface tension caused by the presence of excess charge on the droplet surface. Experiments were successfully interpreted in light of an absorption model that specifically address the droplet formation and fall and considered the model of Matteson and Giardina (1974) to account the droplet charge effect.

We studied the erosion rate of a horizontal plaster tube in a cold-model bubbling fluidised bed of 510 μm glass beads at different fluidisation velocities and at ambient pressure and temperature. To this end, we developed a new experimental procedure based on the cyclic immersion of a cylindrical probe in a bed kept at incipient fluidisation (U = 1.03 Umf) and we compared the obtained results with those achieved during experiments with the same probe immersed at a fixed position inside the fluidised bed operated in bubbling regime. The new procedure was meant to simulate the impact of the bubbles wake with the probe, providing a simplified physical model for erosion in the bed. We also interpreted the experimental results in light of existing models to describe the overall erosion rate. The analysis of data indicated a clear correlation among surface erosion and bubble wake dynamics. Besides, the new procedure provided a way to address the angular profile of tube erosion caused by the exposure to the wake of a single rising bubble. Once multiplied by the product between bubble frequency and wake length, these data allow reconstructing the angular erosion rate profiles in the range of the fluidisation velocity investigated. This result finds confirmation in the analysis of the pertinent literature concerning the drag coefficients of a horizontal tube immersed in dense and dilute granular flows.

This work reports experimental results on the effects of temperature (25, 45, and 65°C at different relative humidity) on the scrubbing of charged submicron particles by means of cold (25°C) droplets charged with opposite polarity. The aim of the study is to experiment how the capture of particles is influenced by the simultaneous presence of electrostatic and phoretic forces related to the occurrence of thermal and water vapor gradients close to the droplet surface. This information plays an important role in the development of wet electrostatic scrubbing (WES), an emerging technology for submicron and ultrafine particle capture. Tests were performed in a lab-scale system in which the particle laden-gas was scrubbed by a train of identic droplets. Particles were charged by a corona source while droplets are generated by electrospraying. Experiments revealed that for particles larger than about 250–300 nm, there were higher removal efficiencies in nonisothermal conditions, with limited differences...