This study investigates size-dependent interparticle triboelectric charging using a wall-free acoustic levitation platform that enables controlled particle-particle collisions while eliminating wall effects. Collisions between dissimilar materials (HDPE and glass) produced strong, unidirectional charge transfer governed by effective work function differences. In contrast, collisions between similarly sized HDPE particles resulted in weak charge transfer with no consistent polarity. For binary-sized HDPE particles, consistent bipolar charging was observed, with larger particles acquiring positive charge and smaller particles negative charge. Pre-charging experiments showed that sufficiently high initial charge can dominate subsequent charge transfer and suppress size-dependent effects. These results provide direct evidence of interparticle bipolar charging and clarify its role in charge generation and redistribution in fluidized beds, with implications for electrostatic charge mitigation.

The combination of limestone calcination, catalytic methane reforming, and combustion in one reactor (MRCCAL) was previously proposed to achieve autothermal and hydrogen-producing sorbent regeneration for calcium-looping technology. However, this technology was only assessed using kinetic-only simulations. To further evaluate its viability, the present study developed an Eulerian-Eulerian CFD model with full reaction kinetics in a bubbling fluidized bed reactor. Three different operating parameters were studied: the inlet gas velocity, the sorbent to catalyst ratio, and the sorbent calcination extent. CFD simulations demonstrated that increasing the inlet gas velocity increased the H2 production by altering the particle distribution through the bed. Decreasing the catalyst-to-sorbent ratio improved local mixing whereas the catalyst tended to locate at the bottom of the bed where an increased total solid holdup was also found. Sorbents with higher calcination extent led to a decreased CO2 composition in the off-gas whilst increasing the H2 composition. When compared with kinetic-only simulations of a continuous reactor, the CFD results showed a noticeable discrepancy in the gas compositions mainly due to the free gas expansion and the more rigorous calculation of the particle mixing patterns, which were not included in the kinetic simulations. The sharp differences emphasized the importance of hydrodynamics in developing novel processes.

This study examines charging dynamics of HDPE and glass particles in gas-solid fluidized beds, focusing on effects of fluidizing gases, humidity, and reactor grounding. Experiments revealed that charge accumulation in HDPE particles is significantly influenced by breakdown strength of fluidization gas, with argon leading to earlier and lower charge saturation. For glass particles, low saturation charge density results from the balance between weak charge generation and strong charge dissipation, rather than dielectric breakdown. Humidity had a material-dependent effect; it enhanced the charging of HDPE particles but did not impact their final saturation levels, while for glass particles, it promoted charge dissipation. Grounding the column, contrary to common expectations, did not significantly reduce electrostatic charges or alter charging dynamics for either particle type because the particle-particle contact controls charge transfer for dielectric particles. These findings highlight the complex interactions between gas type, humidity, and particle and wall materials, emphasizing the need for tailored strategies to manage electrostatic charges in industrial fluidized bed systems.

A novel autothermal methane-reforming limestone-calcination process is analyzed through thermodynamic and kinetic investigations to yield syngas for direct ammonia production. A comprehensive correlation is developed to determine the required gaseous feed concentrations for near-autothermal reactor operation under varying conditions of temperature, pressure, and nitrogen/oxygen compositions. The study establishes critical operating boundaries to achieve complete limestone calcination while preventing coke formation. The process performance, evaluated through the syngas yield and quality metrics (H-2/CO and H-2/N-2 ratio), demonstrates that the optimal MRC calciner off-gas with a H-2/N-2 ratio of 3 can be produced at moderate CaCO3/CH4 molar feed ratio (0.2-0.3) with air oxygen concentrations around 40 vol%. Kinetic analysis in turbulent fluidized bed reactors reveals that appreciable sorbent calcination (>60 %) can be achieved at industrially relevant conditions (pressures up to 25 bar, temperatures below 900 degrees C), with enhanced performance at elevated temperatures and reduced pressures. The process generates syngas primarily composed of H-2, CO, and N-2 at tunable compositions, suitable for ammonia synthesis after the reverse water gas shift reaction without requiring cryogenic air separation.

To address the concern of fire and dust explosions in wood processing facilities, the charging behavior on wood dust particles and air hoses during the air-blow cleaning operation were investigated. The effective work function, unit weight and surface roughness were key parameters influencing the charge accumulation on air hoses. The use of compressed air with lower velocity and higher moisture content could reduce the charge generation on airborne wood particles. Particle size, shape and wood species affect the charging behavior of wood dust. Conductive surface and moisture could help charges to be dissipated fast from wood dust particles.

Transient local solid tracer concentration distributions were measured by a novel, simple and accurate measurement system with fast response to obtain axial solids dispersion in the riser of a circulating fluidized bed operated at solids fluxes up to 450 kg/m(2)s and gas velocities up to 8 m/s. Phosphorescent-coated FCC particles were used as the tracer which were activated by high intensity UV light and injected into the return leg of high-density circulating fluidized bed unit. A radially non-uniform axial dispersion model was utilized to determine axial solids dispersion coefficients, and the results were interpreted with the help of hydrodynamic data obtained in the same column. Comparison of the axial dispersion coefficients at different operating conditions revealed that dispersion decreases when solids circulation flux increases to 450 kg/m(2)s together with the increase in gas velocity to 8 m/s. Low solids dispersion coefficients (D-az < 0.1) at high solids circulation fluxes and high velocities resulted from the disappearance of the net downward flow of particles at the riser walls, signifying the existence of the dense suspension upflow regime.

The charges acquired by polyethylene and glass particles fluidized by argon, nitrogen, and air at different humidity levels in acrylic and steel columns have been measured. Increased bed expansion at higher fluidization gas velocities lowered the space charge effect, allowing the particles to acquire more charges. The low dielectric strength of argon limits the extent of charging when the particles are fluidized in argon. The effect of the humidity of the air on particle charge differed appreciably between the two columns. The charge densities acquired by the particles in several experiments appear to have been limited by the dielectric strength of the fluidization gas.

In this work, particle circulation and separation of binary solids were investigated in a novel fluidized bed system, constructed with two sections connected through a slit. One side contains a vigorously fluidized bed with an inclined distributor for biomass pyrolysis, while the other provides for a gentle fluidized bed for particle separation. Particle exchange through the slit was observed and analyzed by PIV to explain the driving force transporting particles between sections. An inclined distributor facilitated smooth transportation of particles to the gentle bed where the lower-density char was effectively removed from the denser bed materials. Particle transportation, and therefore, particle separation, depended on the gas flow rate into the lower end of the inclined distributor plate and was sensitively affected by the location of the slit. The driving forces of particle transport through a slit were, the instantaneous local pressure difference induced by babbles and also hydraulic head difference.

Electrostatic charge density and the wall coverage of polyethylene and glass particles fluidized by different types of gases (air, nitrogen and argon) were investigated in a transparent acrylic fluidization column via digital image analysis. Compared to other tested gases, argon generated the least degree of wall fouling, indicating that the dielectric breakdown of fluidizing gas is a significant factor that affects the charge buildup on fluidized particles. For polyethylene particles, the degree of wall fouling was strongly correlated to the charge density of the bed particles. However, such a correlation for glass particles is much weaker. Interestingly, the moisture content in the fluidizing gas has a more significant effect on wall fouling for glass particles than that for polyethylene particles, possibly due to the adsorbed water layer on the hydrophilic surface of glass particles. Moreover, the size of particles coated to the wall in all tests was generally smaller than that of the bed particles, indicating that highly charged small particles had a high tendency to attach to the column wall.

This work presents a new dynamic modelling approach for calcium looping systems that allows explicit sorbent deactivation and purge/makeup. These are common in plant operations, but often neglected in modelling. This model adopts a Monte Carlo approach, tracking merely 100 particles between the carbonator and the calciner for 60 reaction cycles with the particle residence time in each reactor determined stochastically. The simulated results agree well with the experimental data in both the transient and steady-state stages. This model provides a promising approach to predicting the dynamic behaviour of calcium looping systems under relatively realistic conditions at low computational cost. The stochastic description of a multiphase reactor via the Monte Carlo process can be widely adapted in various scenarios.

This work assesses and examines particle sedimentation behaviors for magnesium removal process in a commercial lithium recovery plan with the aid of a lab-scale stirred tank reactor in the presence and absence of rotational stirring. The effects of stirrer agitation rate on the sediment height and induction period were investigated in the range of 280-390 RPM. A one-dimensional unsteady-state model was utilized, capable of describing the main phenomena observed in experimental particle sedimentation tests. The model showed fair agreement with experimental results obtained for the batch-wise sedimentation at different agitation rates. Moreover, the model was further used to assess the particle sedimentation behaviors in batch-wise and continuous stirred tank reactors. A critical boundary, based on a critical Peclet number and initial solid volume fraction, was proposed to avert/decelerate particle sedimentation in both reactor configurations, which could provide operation guidelines for batch and continuous reactors. (C) 2022 Elsevier Ltd. All rights reserved.

Fly ash produced from incineration of municipal solid wastes (MSW) contains heavy metals, such as Cd and Pb, that make this material difficult to manage and dispose of safely. Because the composition of fly ash is similar to cement raw meal, partial replacement of raw meal with fly ash may be a feasible way to reduce the health and environmental hazards of the ash, provided that the heavy metals can be effectively stabilized in the solid phase. This research employs proprietary thermochemical software to simulate the thermodynamic behavior and single-step fixation of Cd and Pb in industrial cement kilns. The effect of Cd, Pb and Cl loadings on the fixation and/or evaporation of Cd and Pb during the sintering process is analyzed using data from industrial cement kilns. A simplified model is created based on elemental mass balance to evaluate multi-step fixation of Cd and Pb with cement kiln dust recycle.The results indicate that Cd forms Cd(OH)2(g) in a highly alkaline environment, while nearly 90% Pb is volatilized as PbCl2(g). In the clinker, increased Cl-1 decreased the proportion of Pb and Cd, moreover, Pb and Cd increased in kiln dust with Cl-1 increased; Calculations using a kiln dust recycle model showed that, the concentrations of Pb and Cd in both kiln dust and clinker increased sharply after recycling of kiln dust in steady state. Under unstable conditions, the concentrations of Pb and Cd in kiln dust increased, as well as the heavy metals re-entering the cement kiln.

An iron-based catalyst from bauxite residue (aka BR and red mud) was developed for removing biomass gasification tar. Its performance was investigated with naphthalene as the model tar compound. This was achieved by measuring the catalytic naphthalene conversion at five space velocities and at four temperatures in the 500 degrees C to 800 degrees C range, both in a N(2)environment and in 13 vol% H(2)with the balance N(2)for 14 hours to determine the long-term performance. The physical and chemical characteristics of the catalyst were studied prior to and after exposure to naphthalene to track the evolution of the catalyst as a result of the chemical reaction. In addition, the effects of calcination temperature and reduction with H(2)on the surface characteristics were investigated. The bauxite residue catalyst was shown to be significantly active for naphthalene cracking, with its activity comparable to that of an industrial Ni catalyst. Activity measurements over 14 hours of testing showed that the catalyst activity decreased from 98% to 65% naphthalene conversion with time as a result of catalyst deactivation when tested in a N(2)reaction environment. In the presence of 13 vol% H-2; however, the activity maintained >95% conversion for the entire duration of the experiment.

This paper investigates the effect of calcination temperature and duration on the cyclic CO2 capture performance of natural lime-based sorbents. Tests showed that increasing calcination temperature considerably reduced the sorbent reactivity over the first few calcination-carbonation cycles. No significant variation in performance was observed when a sorbent remained at the calcination temperature after completing limestone decomposition. On the other hand, incomplete limestone calcination significantly altered the sorbent cyclic utilization and CO2 carrying capacity. A semi-empirical method is proposed to estimate the fast reaction-controlled carbonation extent at different reaction cycles, calcination extents and temperatures. This method is shown to work well for two different naturally-derived limestones exposed to different calcination conditions.

A jet attrition model is developed to predict the evolution of the particle size distribution in fluidized beds. This model predicts changes in particle size distribution due to impact attrition in the jet region as a function of operating parameters - temperature, particle impact velocity and time. The model provides good agreement with experimental results for iron and hematite as oxygen carriers, with limestone and lime as CO2 sorbent at temperatures from 20 to 800 degrees C and jet velocities from 59 to 221 m/s. It is found that fragmentation, abrasion, and material fatigue over the attrition duration must be considered. Two fitting parameters considering fatigue by material properties and repeated collisions are applied in this model, with their values determined based on nonlinear least squares regression following the evolution of the particle size distribution.

Fluidized bed bioreactors are widely used in wastewater treatment applications. Such reactors employ gel beads or hard particles covered with a biofilm layer. These particles lose more energy due to deformation when they collide than particles with high mechanical resistance. This energy loss can result in heterogeneity in particle distribution, increasing the drag on them, which, if not considered properly, can lead to problems in reactor design and operation. Therefore, it is important to know how much energy is dissipated by particles with low mechanical strength during collisions. In this context, the coefficient of restitution of alginate particles synthesized using different cationic solutions was determined experimentally. The influence of the Young’s modulus, size and roughness of the particles, as well as the impact velocity, on the coefficient of restitution was investigated. Results indicate that the coefficient of restitution is directly proportional to the particle Young's modulus and inversely proportional to the impact velocity. A correlation is proposed to estimate the coefficient of restitution as a function of particle density, Young’s modulus, impact velocity and maximum deformation in the elastic regime, with R2 = 0.9219. This correlation provides a potential tool for determining the coefficient of restitution to be used in simulating the dynamics of the flow in fluidized bed bioreactors in wastewater treatment.

Landfill leachate is exposed to sunlight through on- and off-site leachate treatment and disposal to surface water bodies. Very little is known about the potential phototransformation of fluorotelomer compounds in landfill leachates, which can undergo environmental oxidation and produce perfluorocarboxylic acids (PFCAs). This study investigated phototransformation of spiked 6:2 fluorotelomer sulfonate (FTS) (∼ 100 μg/L) in leachate under simulated sunlight, using a metal halide lamp (wavelength, 390 to 750 nm). To understand the effects of nitrate and humic acid (HA), phosphate buffer (pH 7.1) containing nitrate and HA were spiked with 6:2 FTS and irradiated under simulated sunlight for 72 h. Following irradiation, 6:2 FTS and known transformation products (i.e., PFCAs) were quantified in the samples using LC-MS/MS. The results showed that 6:2 FTS was undergoing indirect photolysis in leachate (half-life of ∼ 15 days), suggesting that indirect photolysis of 6:2 FTS is likely a relevant transformation pathway in sunlit aquatic environments. However, the spiked 6:2 FTS did not show any observable decrease in the presence of nitrate and HA over 72 h. Perfluorohexanoic acid (PFHxA) increased in irradiated leachate background samples (without 6:2 FTS spike) suggesting that phototransformation in sunlit leachate could lead to the formation of persistent PFCAs at environmental concentrations of the precursors. Future studies using probe compounds are recommended to better understand the roles of reactive species in phototransformation of 6:2 FTS.

Consumer products containing fluorotelomer polymers are a source of fluorotelomer compounds to the environment following their disposal at landfills. The fate and transformation of fluorotelomer compounds are unknown in landfill leachates. This study investigates the aerobic biotransformation of 8:2 fluorotelomer alcohol (FTOH) and 6:2 fluorotelomer sulfonate (FTS) in landfill leachate-sediment microcosms using batch tests. Spiked 8:2 ITOH, 6:2 FTS and their known biotransformation products were quantified in sediment-leachate and headspace over 90 days under aerobic conditions. 8:2 ETON and 6:2 FTS biotransformation was slow (half-life >>30 d) in landfill leachate-sediment microcosm, suggesting persistence of fluorotelomer compounds under the conditions investigated. Significant volatilization (>20%) of 8:2 FTOH was observed in the microcosm headspace after 90 days. C6 - C8 and C4 - C6 perfluorocarboxylic acids (PFCAs) were the most abundant products for 8:2 FTOH and 6:2 FTS, respectively. PFCAs accounted for 4-9 mol% of the initially spiked parent compounds at 90 days. Perfluorooctanoic acid (PFOA) was the single most abundant product of 8:2 FTOH (>2.8 mol% at 90 days). The unaccounted mass (20 to 35 mol%) of the initially spiked parent compounds indicated formation of fluorotelomer intermediates and sediment-bound residue. Overall the findings suggest that aerobic biotransformation of fluorotelomer compounds acts as a secondary source of long- and short-chain (<= C7) PFCAs in the environment. Partitioning of semi-volatile fluorotelomer compounds (e.g.. 8:2 FTOH) to the gas-phase indicates possible long-range transport and subsequent release of PFCAs in pristine environments. Short-chain fluorotelomer replacements (e.g.. 6:2 FTS) result in a higher abundance of short-chain PFCAs in landfill leachate. Future research is needed to understand the long-term exposure effects of short-chain PFCAs to humans, aquatic life and biota. (C) 2020 Elsevier B.V. All rights reserved.

Polycyclic aromatic hydrocarbons (PAHs), abundant in mixed contaminant sites, often coexist with heavy metals. The fate and remediation of PAHs depend heavily on the sorption and desorption behavior of these contaminants. The sorption behavior can in turn be highly affected by certain soil components and properties, such as soil organic matter (SOM) and the presence of heavy metals. Through review of the literature focused on research from 2006 to 2018, this paper discusses interactions, challenges, influencing factors and potential synergies in sorption/desorption of mixed PAHs and heavy metal contamination of soil. The presence of either natural organic matter or heavy metals can enhance the sorption capability of fine soil, retarding the PAHs in the solid matrix. The co-existence of SOM and heavy metals has been reported to have synergistic effect on PAHs sorption. Enhanced and surfactant desorption of PAHs are also affected by the presence of both SOM and metals. Remediation techniques for PAHs removal from soil, such as soil washing, soil flushing and electrokinetics, can be affected by the presence of SOM and heavy metals. More detailed studies on the simultaneous effects of soil components and properties on the sorption/desorption of PAHs are needed to enhance the effectiveness of PAHs remediation technologies.