Sound Assisted Fluidized Bed Research Articles

Corrigendum to “Simulation of cohesive particle motion in a sound-assisted fluidized bed” [Powder Technology 207 (2011) 65–77

We find some mistakes in the operating conditions or the parameter units of Table 1 and some figures of our article published in Powder Technology. (Wang Shuai, Li Xiang, Lu Huilin⁎, Liu Guodong, Wang Jiaxing, Xu Pengfei. Simulation of cohesive particle motion in a sound-assisted fluidized bed, Powder Technology 207 (2011) 65–77). Thus, we send a corrigendum for correction. If need more requirements, please let me know as soon as possible.

Heat Transfer Analysis in Sound-Enhanced Fluidized Beds Containing Geldart B-C Binary Mixtures

An experimental study was carried out on the binary mixing behaviour of Group C with Group B particles as well as the heat transfer behaviour between the bed and submerged heating tube in an acoustic field. The effects of excessive air velocity, sound pressure intensity, and local and averaged heat transfer coefficient were studied for five binary mixes. Different binary mixture fluidization ratios with and without sound aid are used to compare the results. The study also discusses the measurement techniques used, including pressure measurements and the characteristics of the bed solids. Sand and hydrophilic bituminous coal are used as the binary mixture materials, with different proportions of each. The experiments are conducted both with and without acoustic assistance to compare the outcomes. This study provides insights into the heat transfer behavior and binary mixing in a sound-assisted fluidized bed. The findings indicate that sound assistance has a significant impact on the heat transfer performance of Geldart B-C binary mixtures in fluidized beds. It highlights the potential benefits of using acoustic energy to improve fluidization quality in binary systems.

Carbonation Kinetics of Fine CaO Particles in a Sound-Assisted Fluidized Bed for Thermochemical Energy Storage

The calcium-looping process, relying on the reversible calcination/carbonation of CaCO3, is one of the most promising solution to perform thermochemical energy storage (TCES) for concentrating solar power (CSP) plants. Indeed, CaO precursors such as limestone can rely on the high energy density, low cost, large availability and nontoxicity. In this work, the study of the sound-assisted carbonation of fine CaO particles (< 50 μm) for TCES-CSP has been furthered. In particular, a kinetic study has been performed to analyze the effect of the particular carbonation conditions to be used in TCES-CSP applications, i.e. involving carbonation under high CO2 partial pressure and at high temperature. All the experimental tests have been performed in a lab-scale sound-assisted fluidized bed reactor applying high intensity acoustic field with proper frequency (150 dB–120 Hz). The carbonation kinetics has been analyzed by applying a simple kinetic model, able to properly describe the fast (under kinetic control) and slow (under diffusion control) stage of the reaction. In particular, the reaction rate, the intrinsic carbonation kinetic constant and the characteristic product layer thickness have been evaluated, also highlighting their dependence on the temperature between 800 and 845 °C; a value of 49 kJ mol−1 has been obtained for the activation energy. Finally, a good agreement between the conversion-time profiles, evaluated from the applied kinetic models, and the experimental data has been obtained.

Sound-Assisted Fluidization for Temperature Swing Adsorption and Calcium Looping: A Review.

Fine/ultra-fine cohesive powders find application in different industrial and chemical sectors. For example, they are considered in the framework of the Carbon Capture and Storage (CCS), for the reduction of the carbon dioxide emissions to the atmosphere, and in the framework of the thermochemical energy storage (TCES) in concentrated solar power (CSP) plants. Therefore, developing of technologies able to handle/process big amounts of these materials is of great importance. In this context, the sound-assisted fluidized bed reactor (SAFB) designed and set-up in Naples represents a useful device to study the behavior of cohesive powders also in the framework of low and high temperature chemical processes, such as CO2 adsorption and Ca-looping. The present manuscript reviews the main results obtained so far using the SAFB. More specifically, the role played by the acoustic perturbation and its effect on the fluid dynamics of the system and on the performances/outcomes of the specific chemical processes are pointed out.

Effects of sound fields on hydrodynamic and dry beneficiation of fine coal in a fluidized bed

The difficulty of forming a stable fluidized bed for fine coal (<1 mm) reduces the effectiveness of the density-segregation process and subsequent dry beneficiation of fine coal. Sound fields provide a new method of improving the bed stability of fine coal. In this study, the hydrodynamic and dry beneficiation of fine coal under a sound field was investigated by a numerical simulation and an experiment. The results indicate that when the sound frequency f (or sound pressure level SPL) is increased, the fluidization characteristics of the bed significantly improve, although the increased sound absorption coefficient weakens the positive effects of the sound field on the fluidization characteristics under high frequencies (f > 120 Hz). Moreover, the simulation results indicate that the introduction of the sound field eliminates large bubbles at a high gas velocity, resulting in an expansion of the gas velocity range for the efficient density segregation process of fine coal. Finally, under appropriate operating conditions (f = 120 Hz, SPL = 120 dB, u = Umf), fine coal was separated in a sound-assisted fluidized bed, with probable error E values as low as 0.11 g/cm3, where the clean coal yield was 52.20% with an ash content of 23.28%; the yield of gangue products was 47.80% with an ash content of 47.80%, demonstrating the efficient beneficiation of fine coal in a sound-assisted fluidized bed.

Bed expansion characteristics in sound assisted fluidization of Geldart's group A powder

Intrinsic bed expansion characteristics in a sound assisted fluidization of Geldart's group A powder were investigated. To obtain an accurate bed expansion data, a 1-valve and 2-valve bed collapse experiment, together with a bed collapse model for a correct interpretation of bed collapse curves, was used. It was found that a total bed voidage and a dense phase for the sound assisted fluidization were varied with an inlet superficial velocity in the same fashion as those for a conventional fluidization. Besides, the voidage with respect to the inlet superficial velocity of the sound assisted fluidization was found to be lower, in comparison with those of the conventional fluidization and was independent on a sound frequency. On the other hand, dense phase voidage and its superficial velocity relations of the sound assisted fluidization at the different sound frequencies were approximately on the same trend as that for the conventional fluidization. And, a minimum bubbling point, defined using the dense phase voidage and the dense phase superficial velocity characteristic curve, was also unaffected by the sound vibration force. These findings suggested that the sound vibrational force tended to create more cavity or bubble phase in the fluidized bed, rather than changing a hydrodynamics relation in the dense phase. Therefore, the same equilibrium of force as that of the conventional fluidization can still be applied for the sound assisted fluidization, as well as stability criteria. Finally, it was proved that the modified revised Ergun drag force correlation, applicable for the conventional fluidization, can describe well the dense phase voidage and the dense phase superficial velocity characteristic curves of the sound assisted fluidization. Likewise, the stability criterion, proposed by Cherntongchai and Brandani in 2013, can predict excellently the minimum bubbling points for the sound assisted fluidized bed.

A comparison between interparticle forces estimated with direct powder shear testing and with sound assisted fluidization

Understanding the role of the interparticle forces in fluidization of cohesive powders is crucial for a proper application of fluidization to these type of powders. However, a direct measure of the interparticle interactions (IPFs) is challenging, mainly because cohesive particles cannot be fluidized under ordinary conditions. That is the reason why IPFs are typically measured using a rheological approach. The aim of this study is, therefore, to evaluate the IPFs of cohesive powders under actual fluidization conditions, by using an experimental and theoretical approach. In particular, a sound assisted fluidized bed apparatus was used to achieve a fluidization regime of the particles. Then, the cluster/subcluster model was applied to calculate IPFs, starting from the experimental data. The obtained IPFs were then compared to those evaluated by using a shear testing approach.

CO2 adsorption on a fine activated carbon in a sound assisted fluidized bed: Thermodynamics and kinetics

Combustion of fossil fuels is one of the major sources of CO2, it is therefore necessary to develop technologies that will allow to utilize fossil fuels while reducing CO2 emissions to the atmosphere. Removal of CO2 from flue gases has become an effective way to mitigate CO2 emissions and adsorption is considered to be one of the methods. In particular, adsorption on fine and ultra-fine sorbents in a sound assisted fluidized bed has been proved to be a promising alternative, being able to maximize CO2 adsorption capacity and kinetics. However, before the design of an adsorption equipment, investigation of equilibrium and kinetics plays a decisive role.In this work, the previous research was furthered into the investigation of the mechanism (isotherm), nature/strength (thermodynamics) and rate (kinetics) of CO2 adsorption on a commercial activated carbon in a sound assisted fluidized bed. Langmuir and Freundlich equations were used to model the CO2 adsorption isotherm in the low pressure region (i.e. typical of a combustion flue gas). The results revealed that Freundlich equation was more accurate for predicting the adsorbed amount than the Langmuir one, which indicates a heterogeneous surface binding. Then, adsorption behavior was elucidated by energy function such as standard Gibbs free energy, enthalpy and entropy, suggesting the spontaneity and feasibility of adsorption of CO2 by activated carbon, and its exothermic and physical nature. The isosteric heat of adsorption was also evaluated; its decrease with surface loading further indicated the heterogeneity of adsorption sites and also variation in adsorbate–adsorbent interactions. Finally, this study also presented a kinetic analysis of CO2 adsorption, from which CO2 binding on activated carbon was deduced to follow pseudo-first order kinetic.

Experimental analysis and computational fluid dynamics simulations for heat transfer in sound assisted fluidized bed of fine powders

Fine powders in the size range of 20-200 ?m are widely used in industries for fluid bed operations and are ideal for gas-solid reactions because of their large external surface areas and favorable heat transfer rates. The fine powders have very poor flow characteristics. Most of the earlier research work in heat transfer in bubbling fluidized beds is focused on coarse grained Geldart B and D particles. Acoustic energy of sufficient intensity and sound pressure level improved the quality of fluidization of fine powders. The objective of this investigation is experimental analysis and CFD simulations for heat transfer in a fluidized bed of fine powders at different acoustic conditions. The Eulerian approach has been identified as an efficient method for the numerical simulation of fluidized beds. The experimental and CFD results are in good agreement with each other.

On improving the CO2 recovery efficiency of a conventional TSA process in a sound assisted fluidized bed by separating heating and purging

Carbon capture from point source emissions has been recognized as one of several strategies necessary for mitigating release of greenhouse gases (GHGs) into the atmosphere. Though several CO2 capture technologies have been proposed, temperature swing adsorption (TSA), consisting in adsorbing the CO2 and, then, recovering it by a temperature increase and gas purge, is currently believed to be one of the most promising for post-combustion applications. With reference to the sorbent, great attention is focused on fine powders. Indeed, sorbent in the form of fine powders can be the substrate to realize new highly specific materials whose properties can be tuned at a molecular level and, besides that, most of the commercial adsorbent materials are generally available in the form of fine powders. Previous works successfully verified the feasibility of carrying out TSA adsorption/desorption cycles in a sound assisted fluidized bed, thus enhancing the performances of the entire cyclic process. The focus of the present work is to overcome the main drawback of a conventional TSA, namely the dilution of CO2 in the purging gas, by changing the traditional heating method. To this aim, a separate heating and purge regeneration strategy, consisting in desorbing part of the CO2 by the sole thermal effect, has been tested on a commercial activated carbon, thus eliminating the unavoidable dilution effect caused by purge, and the remainder reducing the CO2 partial pressure. Heating is very efficient for desorbing CO2. Indeed, 80% of the captured CO2 can be recovered at a moderate temperature of 130 °C.

An Innovative Method to Produce Metal Foam Using Cold Gas Dynamic Spray Process Assisted by Fluidized Bed Mixing of Precursors

Metallic foams are known for their interesting physical and mechanical properties such as high stiffness, very low specific weight, high compression strength, unusual acoustic and thermal properties and good energy absorption characteristics. These materials are currently manufactured by means of several different processes. The limit of these conventional technologies is the impossibility to produce foams with complex geometry.This paper deals with the study of an innovative method to produce complex shaped precursors for aluminum foams through cold gas dynamic spray deposition process (CGDS). Aluminum alloy (Al-Si) fine powders were previously mixed with the blowing agent (titanium-hydride, TiH2). The mixing process was carried out by means of sound-assisted fluidized bed apparatus that allows to obtain an homogeneous mixture of the two elements. The mixed particles were then sprayed by means of the CGDS process on a stainless steel sheet that simulates the real component to be reinforced with the foam. Subsequently the obtained precursor was heated up in a furnace The produced metal foam was characterized using optical and electron microscopy in order to study the cell morphology and distribution.The obtained results showed the effectiveness of this method to produce aluminum foams with complex shape.

Effect of acoustic field on CO2 desorption in a fluidized bed of fine activated carbon

Adsorption using solid sorbents has the potential to complement or replace current absorption technology, because of its low energy requirements. Among the commercially available adsorbent materials, attention is focused on activated carbons because they are easily regenerable by reason of their low heat of adsorption. These sorbents are generally available in the form of fine powders. Sound-assisted fluidization can process large amounts of fine powders, promoting and enhancing CO2 capture on fine sorbents, because it maximizes gas–solid contact. Temperature swing adsorption (TSA), consisting of inducing sorbent regeneration and CO2 recovery by appropriate temperature increase and gas purge, is one of the most promising techniques. This study investigates the CO2 desorption process by TSA in a sound-assisted fluidized bed of fine activated carbon. Desorption tests were performed under ordinary and sound-assisted fluidization conditions to assess the capability of sound to promote and enhance the desorption efficiency in terms of CO2 recovery, CO2 purity, and desorption time. The results show that the application of sound results in higher desorption rates, CO2 recovery and purity. Regular and stable desorption profiles can be obtained under sound-assisted fluidization conditions. This stability makes it possible to successfully realize a cyclic adsorption/desorption process.

Effect of operating conditions on the CO2 recovery from a fine activated carbon by means of TSA in a fluidized bed assisted by acoustic fields

CO2 temperature swing adsorption (TSA), consisting in adsorbing the CO2 and, then, inducing the sorbent regeneration and CO2 recovery by a temperature increase and gas purge, is a promising strategy for CO2 capture. With reference to the sorbent, commercially available adsorbent materials are generally available in the form of fine powders. A sound-assisted fluidized bed is capable of fully exploiting the potential and properties of fine sorbents, due to large gas–solid contact efficiency, high rate of mass/heat transfer and low pressure drops. This work is focused on the CO2 desorption process by TSA in a sound-assisted fluidized bed of fine activated carbon. The effect of desorption temperatures and N2 purge flow rate on the regeneration efficiency has been assessed in terms of CO2 recovery level and purity and desorption time. Both of them positively affect the desorption process in terms of enhanced desorption kinetics. Increasing temperatures also yield higher CO2 purities, whereas, no remarkable dilution effect has been observed when increasing the N2 flow rate. Finally, the activated carbon keeps its performances over 16 adsorption/desorption cycles, due to the stability of the regeneration process under sound-assisted fluidization conditions.

Effect of acoustic field on minimum fluidization velocity and drying characteristics of lignite in a fluidized bed

The fluidization and drying characteristics of Shengli lignite in a sound-assisted fluidized bed are investigated. The effects caused by sound frequency and sound pressure level on the minimum fluidization velocity and drying rate are studied. Experiments indicated that acoustic field can improve the fluidization quality and drying rate of Shengli lignite. The minimum fluidization velocity decreased with an increase in sound pressure level and has a minimum value at a sound frequency of 1.5 kHz. The drying rate of Shengli lignite was especially increased during the initial period of the drying process, while the effect was minor toward the end of process. Based on the determination of TG, FTIR, and BET, the structure changes of Shengli lignite were measured to assess the changes in the quality of dried lignite with the assistance of acoustic field. The weight loss rate of dried lignite decreased with the introduction of acoustic waves. Total pore volume, average pore diameter, and specific surface area were significantly reduced with introducing acoustic waves. Carbonyl decreased progressively with the assistance of acoustic field while carboxyl and hydroxyl increased and decreased thereafter. In addition, the energy consumption of fluidized bed drying system after inducing acoustic field is investigated.

CO2 capture performances of fine solid sorbents in a sound-assisted fluidized bed

Post-combustion CO2 capture processes have the greatest near-term potential for reducing greenhouse gas emissions because these processes can be retrofitted to existing units, thus providing a quicker solution to mitigate CO2 environmental impacts. Among all the post-combustion technologies, adsorption processes on solid sorbents are attractive due to their low energy requirements. Great interest is focused on ultra-fine materials, whose chemico-physical properties can be tuned at the molecular level. In this framework sound-assisted fluidization has already been proved to maximize the CO2 adsorption capacity of fine sorbents with respect to common technologies, due to the higher exploitation of the exposed surface. The aim of the present work is, therefore, to compare the adsorption performances of different materials (two activated carbons, two zeolites and a metal organic framework) under sound-assisted fluidization conditions (140dB–80Hz) in order to maximize the gas–solid contact efficiency and, in turn, minimize the limitations to the intrinsic adsorption capacity of the sorbents. All the tests were performed at ambient temperature and pressure with values of CO2 concentration typical of flue gases (5–10vol.%). The different behaviors exhibited by the materials were explained on the basis of their textural properties. In particular, the microporosity falling in the range of 8.3–12Å strongly affects the CO2 adsorption performances under the investigated operating conditions.

Magnetite loaded carbon fine particles as low-cost CO2 adsorbent in a sound assisted fluidized bed

CO2 adsorption with solid sorbents is one of the most promising options for post-combustion CO2 capture strategies. Typical post-combustion flue-gas conditions are CO2 1–15%vol. and atmospheric pressure and the performances of solid sorbents under typical flue gas conditions have been poorly investigated. In that condition the CO2 uptake capacity is influenced primarily by material functionality effects rather than material pore metrics so materials with a distinctive surface chemistry (presence of activated surface atoms or sites) could find applications in adsorption technologies. Hence the sorbent selection became a key point because the materials should be convenient from the economic point of view but versatile in post-combustion conditions. Recent studies of CO2 adsorption on low-cost iron metal oxide surfaces strongly encourage the possible use of metal oxide as sorbents, but the tendency of magnetite particles to agglomerate causes a lowering of CO2 uptake capacity. The dispersion of magnetite nanoparticles on carbonaceous matrix appears to be a promising strategy to overcome this shortcoming. This work investigates the adsorption behavior of CO2 on composite materials prepared coating a low-cost commercial carbon black (CB) with magnetite fine particles. The CO2 capture capacity of composites produced at different CB load was evaluated on the basis of the breakthrough times measured at atmospheric pressure and room temperature in a lab-scale fixed bed micro-reactor. A CB–FM composite has been selected to verify the possibility of carrying out a two-stage operation and the thermochemical stability in a sound assisted fluidized bed. To this aim the reactor has been firstly operated for CO2 adsorption and then for regeneration. The effect of multiple cycles of adsorption and desorption steps has been also quantified.

CO2 capture performance of HKUST-1 in a sound assisted fluidized bed

Among the CCS technologies, adsorption processes are attractive due to their low energy requirements, stimulating recent research to find suitable and highly specific adsorbents for removing CO2 from flue gas. Much attention has been focused on metal–organic frameworks (MOF), a new class of microporous materials that have potential applications in separation processes. As regards the handling of such fine materials, sound-assisted fluidization has been indicated as one of the best technological option to improve the gas–solid contact by promoting a smooth fluidization regime. The present work is focused on the CO2 capture by sound assisted fluidized bed of a specific MOF, HKUST-1. Tests have been performed in a laboratory scale experimental set-up at ambient temperature and pressure, pointing out the effect of sound parameters (intensity and frequency) and CO2 partial pressure. Effectiveness of CO2 adsorption has been assessed in terms of the moles of CO2 adsorbed per unit mass of adsorbent, the breakthrough time, the adsorption rate and the fraction of bed utilized at breakpoint. The results show the capability of the sound in promoting a more efficient adsorption process. Finally experimental tests have been carried out to find a possible regeneration strategy of the sorbent. The stability of the material has been assessed performing different chemico-physical characterizations (BET, XRD, TG, FT-IR and granulometric distribution) on a sample of HKUST-1 subjected to 10 CO2 adsorption/desorption cycles.

CO2 adsorption on fine activated carbon in a sound assisted fluidized bed: Effect of sound intensity and frequency, CO2 partial pressure and fluidization velocity

Among all the CCS strategies, post-combustion capture provides a near-term solution for stationary fossil fuel-fired power plants, eliminating the need for substantial modifications to existing combustion processes and facilities. In this respect, adsorption using solid sorbents has the potential, in terms of energy saving, to complement or replace the current absorption technology. Therefore, the design of highly specific CO2 adsorbents materials is requested. In this framework, great interest is focused on nanomaterials, whose chemico-physical properties can be tuned at the molecular level. As regards the handling of such materials, sound-assisted fluidization is one of the best technological options to improve the gas–solid contact by promoting a smooth fluidization regime. The present work is focused on the CO2 capture by sound-assisted fluidized bed of fine activated carbon. Tests have been performed in a laboratory scale experimental set-up at ambient temperature and pressure, pointing out the effect of CO2 partial pressure, superficial gas velocity, sound intensity and frequency. Effectiveness of CO2 adsorption has been assessed in terms of the moles of CO2 adsorbed per unit mass of adsorbent, the breakthrough time and the fraction of bed utilized at breakpoint. The results show, on one hand, the capability of the sound in enhancing the adsorption process and, on the other hand, confirm that sound assisted fluidization of fine solid sorbents is a valid alternative to the fixed bed technology, which require also an additional previous step of pelletization.

Photocatalytic degradation of formaldehyde in a fluidized bed with sound-magnetic assistance

The photocatalytic degradation of formaldehyde in a sound-magnetic assisted fluidized bed (SMFB) was investigated using Degussa P25 catalyst and Fe3O4 particles as the fluidized media. The effects of magnetic induction, sound pressure level, and sound frequency on the degradation rate of formaldehyde were investigated. Compared with fluidized bed (FB), sound assisted fluidized bed (SFB), magnetic assisted fluidized bed (MFB), SMFB could enhance the degradation efficiency of formaldehyde effectively. Experimental results showed that the degradation efficiency of formaldehyde increased with increasing magnetic induction and sound pressure level. The degradation efficiency of formaldehyde increased with increasing sound frequency ranging from 50 to 100Hz, further decreased with increasing sound frequency from 100 to 150Hz. Moreover, it was found that the reaction kinetic fitted the pseudo-first-order kinetic equation, which provided a detailed kinetic understanding of photocatalytic degradation of formaldehyde in SMFB.

Effect of acoustic field on heat transfer in a sound assisted fluidized bed of fine powders

The fluidized beds are widely used in a variety of industries where heat transfer properties of the fluidized system become important for successful operation. Fluidized are preferred in heat recovery processes because of their unique ability of rapid heat transfer and uniform temperature. Fine powders handling and processing technologies have received widespread attention due to increased use of fine powders in the manufacture of drugs, cosmetics, plastics, catalysts, energetics and other advanced materials. A better understanding of fluidization behavior of fine powders is of great importance in applications involving heat transfer, mass transfer, mixing, transporting and modifying surface properties etc. The difficulty in putting the fine powders in suspension with the fluidizing gas is related to the cohesive structure and to the physical forces between the primary particles. The sound waves agitate bubbling and this results in improving solids mixing in the fluidized bed. The improved solids mixing results in uniform and smooth fluidization, which leads to better heat transfer rates in the fluidized bed. The heat transfer for different sized particles at different acoustic conditions, gas velocities and angular positions around the circumference of heat transfer surface was investigated. Optimum fluidization velocities and acoustic conditions to obtain maximum heat transfer rates from the heat transfer surface to the bed material were found out. Most of the research work in heat transfer in bubbling fluidized beds is focused on Geldart B and D particles. Very little information is available for heat transfer with fine powders belonging to Geldart groups C and A category. The heat transfer between a bubbling fluidized bed of fine powders with an immersed heating surface in absence and presence of acoustic waves was investigated. Acoustic energy of sufficient intensity and sound pressure level significantly improved the quality of fluidization of fine powders. Heat transfer rates could be improved by the oscillation of the particles at certain frequencies. The heat transfer intensity strongly depended upon the angular position along the circumference of the heat transfer surface. The location for maximum heat transfer rates was at the sides of the tube and shifted upward at higher gas velocities. Acoustic waves had very little effect on heat transfer for coarse grained particles. However, heat transfer rates improved appreciably for fine powders under acoustic conditions. The data for local and average heat transfer coefficients is presented as a function of excess air velocity and sound pressure level.