Bed Expansion Research Articles

Optimization and dust emissions analysis of the air jigging technology applied to the recycling of construction and demolition waste

This work aims to evaluate the use of the air jigging technique, a density-based separation technology commonly applied in mineral processing, to upgrade the quality of mixtures (density and geometric properties) that represents the typical composition of construction and demolition waste (CDW) produced in Brazil. In this sense, tests involving the variation of the main operational parameters of jigging (bed expansion rate, pulsation frequency and jigging time) were carried out aiming to find those which provided the best recycled aggregates quality after processing. Also, fines and dust emissions generation during jigging were measured in order to estimate their potential impacts on human health and environment. The results showed that the air jigging process is adequate to improve the quality of CDW by increasing the concrete concentration in the dense product. The use of high bed expansion rates showed to be of major importance to decrease the content of ceramic aggregates in the dense product, allowing obtaining products richer in concrete. Also, the measured properties of the obtained aggregates (size distribution, shape, etc) met the usual standards required for natural aggregates. Finally, material losses and dust emissions generated were negligible in comparison to the total mass processed, although special attention must be given to safety measures due the presence of inhalable particles (<10 μm).

Numerical Studies on Teeter Bed Separator for Particle Separation

Teeter Bed Separators (TBS) are liquid–solid fluidized beds that are widely used in separation of coarse particles in coal mining industry. The coal particles settle in the self-generating medium bed resulting in separation according to density. Due to the existence of self-generating medium beds, it is difficult to study the sedimentation of particles in TBS through experiments and detection methods. In the present research, a model was built to investigate the bed expansion characteristics with water velocity based on the Euler–Euler approach, and to investigate the settling of foreign particles through bed based on the Euler–Lagrange approach in TBS. Results show that the separation of in TBS should be carried out at low water velocity under the condition of stable fluidized bed. Large particles have a high slip velocity, and they are easily flowing through the bed into the light product leading to a mismatch. The importance of self-generating bed on separation of particle with narrow size ranges are clarified. The model provides a way for investigating the separation of particles in a liquid–solid fluidized bed and provides suggestions for the selection of operation conditions in TBS application.

The effect of gas properties on Group C+ fluidized bed reactor

The performance of a fluidized bed reactor depends mostly on the fluidization quality, which can be significantly affected by the gas properties, especially the gas viscosity and density. The effects of gas species on the fluidization properties such as minimum fluidization velocity, bed expansion, dense phase voidage, and pressure fluctuation of three typical types of Group C+ (nano-modulated Geldart Group C) particles, were carefully studied using five types of fluidizing gases and their combinations. With the increase of gas viscosity and density, argon possessed the lowest minimum fluidization velocity and the highest dense phase and total bed expansions, followed by air/nitrogen and helium, and trailed by hydrogen. Using two gas mixtures, the gas viscosity was singled out from the gas density and proved to play a more important role on the fluidization due to the increasing gas viscosity causing a more significant increase in the drag force on the particles. The smallest particles, 10 μm glass beads, had stronger cohesion than the 17 μm and 22 μm larger polyurethane particles and therefore exhibited a higher minimum fluidization velocity, lower dense phase and bed expansions, and larger pressure fluctuations.

Characterization of bubble behaviors in a dense phase pulsed gas–solid fluidized bed for dry coal processing

Pulsed gas–solid fluidized beds can effectively separate fine coal, and bubbles play an important role in creating suitable separation conditions. The present study performed statistical and image analyses of the evolution of bubbles in a two-dimensional pulsed gas–solid fluidized bed using a high-speed dynamic camera. The effects of apparent gas velocity, pulsation frequency and particle size on bubble characteristics and bed expansion were analyzed. The results indicate that, when a fluctuation frequency is added, the expansion height of the bed increases, the effect of attachment to the bed wall decreases, the leading diameter and rising velocity of the bubbles both decrease and the degree of bubble deformation increases. These trends are also more obvious for fine particles. These findings demonstrate that a high density pulsed gas–solid fluidized bed can effectively combine gases and solids to produce a uniform, stable mixture. The bubble diameter and rising velocity were also simulated in the present work, and the relationship between the two was established using a fitting model with an error within 5%. This model provides an effective means of predicting bubble velocity as well as studying the distribution of the bubble phase and improving the stability of the bed density.

In-situ neutron imaging study of NH3 absorption and desorption in SrCl2 within a heat storage prototype reactor

Abstract Strontium chloride octaammine Sr(NH3)8Cl2 offers high volumetric and gravimetric NH3 densities and can store and release heat upon exo-/endothermal absorption and desorption of NH3. Thus, it is a promising material for thermochemical heat storage (THS) applications. In the present work, in-situ neutron imaging was applied to analyze spatio-temporal development of Sr(NH3)8Cl2 powder in a thermochemical heat storage prototype reactor during NH3 absorption and desorption processes. The powder was embedded in a stainless steel honeycomb for the efficient heat transfer during the NH3 desorption process. 2D radiography images were obtained during NH3 ab-/desorption cycles at selected temperatures. The swelling and formation of the porous structure in SrCl2 is monitored during the first cycles. A powder bed expansion of up to 10% upon NH3 absorption was observed. Neutron tomography experiment were also performed to acquire 3D information which revealed the deformation of the honeycomb. This neutron imaging experiment brought crucial information for optimizing the design of efficient and safe THS systems.

Experimental and numerical investigation of sands and Geldart A biomass co‐fluidization

AbstractThis article investigated the fluidization of sands and small Geldart A biomass mixtures. The mixture fluidized like Geldart A type particles with a uniform bed expansion regime before bubbling. The video recorded color distance between pure sands and sands–biomass mixtures was used to estimate the sands–biomass mixing. The coarse‐grained computational fluid dynamics–discrete element method with a hybrid drag model which couples the Syamlal–O'Brien drag and a filtered drag can capture the mixing while the simulation with Gidaspow drag predicted a segregated bed. The simulations were further validated with experimental measured pressure drops. The time averaged pressure drop equals the weight of the bed material, however, its fluctuation is about three times of the bed material fluctuation.

Study of Hydrodynamics and Overall Gas Hold Up Validation in Bubble Column by Computational Fluid Dynamics

The study of overall gas hold up has been carried out experimentally with the bed expansion. The superficial gas velocities used for the experiments are 6.369 m/s and 10.616 m/s. The experiment is carried out in a bubble column with inside diameters of 7 cm and a height of 100 cm. Gas from the gas cylinder is supplied through a distributor consisting of a perforated plate and glass beads. The perforated plate has a hole diameter of 1 mm and 0.5 mm. Computational Fluid Dynamic (CFD) using a Eulerian coupled with Population Balance model is developed to predict overall gas hold up and bubble size distribution. The effect of superficial gas velocity, perforated plate diameter, gas properties, and initial liquid level on gas hold up were studied. The use of population balance can significantly improve the overall gas hold-up results compared to constant bubble diameter. It is found that several operating conditions affect the whole gas hold up, namely initial liquid level, superficial gas velocity, and differences in gas properties. While the influence of the difference in perforated plate diameter to overall gas holds up, results are small compared to other operating conditions.

Effect of temperature and apparent liquid viscosity on the hydrodynamics of liquid–solid tapered inverse fluidized bed: experimental studies compared with empirical models

In the present work, immersed heater to bed heat transfer coefficient and related hydrodynamics were determined along with different angles (7.85 and 6.8) of the tapered inversed fluidized bed. Carboxyl methylcellulose was used to change the water viscosity by using a power-law model. The hydrodynamics was compared for two different angles of beds. Furthermore, minimum fluidization velocities were carried out for different liquid apparent viscosities and different angles of beds and compared with previous models. The heat transfer coefficient was found to be increasing with liquid velocity and bed voidage, respectively, and it was also found that the bed voidage is high for a high diameter of particles. The correlation was developed between the bed expansion ratio and independent parameters by response surface methodology in design expert software v.9.

Backwashing behavior and hydrodynamic performances of granular activated carbon blends

Ozone-biological activated carbon (O3-BAC) process has been proved to be an efficient and cost-effective technology in advanced treatment of drinking water. However, O3-BAC raises strict requirements in adsorption, hydrodynamic and regeneration performances, which one single activated carbon could hardly all-sided meet. Blending activated carbons seems to be an appropriate and economically feasible method to deal with the issue. Thus, the uniformity and stability of activated carbon blends during water treatment, especially in backwashing process are of great importance. In this paper, cyclic experiments of downward adsorption and upward backwash on 11 typical commercial granular coal-based activated carbons and their blends were carried out in column test. Hydrodynamic performances such as bed expansion rate and bed pressure drop were measured. The uniformity and stability of activated carbon blends were investigated by determining iodine number of samples collected from different heights of activated carbon bed. Then, both traditional regression methods and back-propagation neural network model were utilized to predict superficial velocity at 30% bed expansion rate and maximum bed pressure drop of activated carbon blends. The results indicate that water backwashing process has no effect on the composition proportion of activated carbon blends, and slightly changes the particle distribution of activated carbon bed regarding pore structure and adsorption capacity. A three-layer back-propagation neural network model for superficial velocity at 30% bed expansion rate yields mean relative errors of 2.17%, which is much lower than that given by traditional regression methods such as 5.53% (weighted average), 4.08% (linear) and 4.06% (polynomial). Moreover, the back-propagation neural network model for maximum bed pressure drop yields mean relative errors of 1.37%, which is much lower than that given by traditional regression methods such as 4.31% (weighted average), 4.28% (linear) and 4.22% (polynomial). The non-linear relationships can be accurately identified by the back-propagation neural network model.

Hydraulic characterisation of the backwash process in sand filters used in micro irrigation

The objective was to evaluate effects of structural design, particle size and filter media height on pressure loss and surface velocity in the expanding filter layer during the backwashing process. The hydraulic behaviour of three commercial sand filter designs were compared. Experiments were conducted in an experimental closed circuit module. The treatments were based on the evaluation of three sand particle sizes combined with three filter bed heights for each filter design. The results showed that for the evaluated sand filters, with their different drainage structures in terms of area and arrangements, had different hydraulic behaviours during the backwashing. Coarser sand particles and greater filter layer heights produced larger slopes in the surface velocity curves as a function of percentage of filter bed expansion. No difference was observed in the minimum fluidisation velocity with changing the filter media heights, but an increase in the minimum fluidisation velocity was observed with increasing sand particle size. Filter beds composed of coarse sand particles and low filter bed heights produced lower increases in the pressure loss with increasing backwash surface velocity. Determining the minimum fluidisation velocity using the graphical analysis method to determine the pressure loss across the filter bed proved to be a reliable method for evaluating the equipment used.

Pretreatment for seawater desalination plants by calcite ooids filter

The calcium carbonate is the main constituent of calcite ooids which are important and often dominant components of marine sediments. In this study, the calcite ooids were fabricated inside a semi-pilot seawater-softening unit assembled in the Egyptian Petroleum Research Institute (EPRI) with an effective particle sizes varying from less than 0.5 up to 3.0 mm. The created calcite ooids were used as new filtration media in pretreatment stage of a seawater desalination plant. A feed water quality improvement was achieved at various temperatures (20–40 °C) and at various speeds (20–60 l/min). Typical operating qualifications of calcite ooids filter in seawater desalination plant are speed of 20 l/min and temperature of 40 °C in the presence of poly-aluminum chloride coagulant, PAC (1.6 mg Al/l). The filtrate produced from ooids filter had a better silt density index (SDI) of 2.85, higher removal of turbidity (89.4%), higher total organic carbons reduction (66.1%) and TOC reduction exceeds to 95.7% after granular activated carbon filter. Therefore, the service and backwash flow rates and bed expansion percentage are the essential operating parameters which were studied.

Multi-fluid Eulerian simulation of fluidization characteristics of mildly-cohesive particles: Cohesive parameter determination and granular flow kinetic model evaluation

The typical granular kinetic model, the cohesive granular kinetic model based on the contact bonding energy (Kim-Arastoopour-Huilin model) and the cohesive granular kinetic model based on the excess compressibility (Ye et al.'s model) were comprehensively compared in terms of kinetic parameters, bed expansion, and bubble behavior. The calculation methods of the contact bonding energy loss and the excess compressibility were presented, and the inter-relationship between the two cohesive parameters was revealed. The three kinetic models predict consistent kinetic parameters in dilute gas-solid flow region, while Ye et al.'s model always predicts a lower value when the solid fraction is above 0.15. The Kim-Arastoopour-Huilin model and Ye et al.'s model predicts opposite variations of solid pressure with increasing cohesion. Increasing cohesion interaction reduces the granular shear viscosity and bulk viscosity. Kim-Arastoopour-Huilin model and Ye et al.'s model outperform the typical kinetic model in terms of the bubble diameter and rising velocity.

Numerical investigation of binary particle mixing in gas-solid fluidized bed with a bubble-based drag EMMS model

Heterogeneous flow structure of bubbling deeply affects gas–solid momentum transfer in a binary gas–solid fluidized bed. This work presented a binary particle bubble-based Energy Minimum Multi-scale (EMMS) model, and an assumption that bubble-emulation drag force acting on solid 1 and solid 2 depending on each solid volume ratio in the emulation phase was applied to simplify the force balance of the binary particle-phase. The bubble-based EMMS drag was incorporated in the Eulerian multi-fluid model to predict the mixing behaviors of two binary particle systems. The simulation results agree well with the experimental observations in terms of binary solid mixing, bed expansion, and bubble diameter. Compared with the prediction results by the Gidaspow drag model, the jetsam solid fraction and bubble size predicted by the present drag model is in more agreement with the measured results, which indicate the EMMS drag model is an alternative choice for modeling binary gas–solid bubbling system.

Fluidization of nanoparticle agglomerates assisted by combining vibration and stirring methods

Fluidization of nanoparticle agglomerates is a promising technology to process nanoparticles, where the nanoparticles always exist in complex agglomerates due to strong interparticle forces. In this study, we propose an assisted method by combing vibration and stirring to improve the fluidization quality of nanoparticle agglomerates. The fluidization behaviors are evaluated in terms of minimum fluidization velocity, bed expansion ratio, and the size distribution of agglomerates, for three kinds nanoparticles of SiO2, Al2O3 and TiO2. The results show that, both vibration and stirring can improve the fluidization quality of nanoparticle agglomerates. However, the fluidization quality is no longer improved, or even worsen when the vibration or stirring parameter exceeds a critical value. Compared with fluidization assisted by vibration or stirring separately, the combination of the two methods can further decrease the minimum fluidization velocity, and increase the bed expansion ratio. More importantly, the segregation of the agglomerate sizes can be significantly reduced by using the combined method. This study provides a new reliable method to assist the fluidization of nanoparticle agglomerates.

Application of the kinetic theory of rough spheres to the simulation of the hydrodynamics of particles and liquid phases in a fluidized bed

The flow behaviors of liquid and particles in a fluidized bed are simulated using a liquid-solid two-fluid model, coupling with the kinetic theory of rough spheres. The expressions for the energy dissipation and viscosities of particles are adopted as functions of the tangential restitution coefficient and the restitution coefficient of particles, which consider the effects of particle rotation on the exchange and dissipation of particle energy. The simulated bed expansion height, particle concentration, particle velocity and total granular temperature differ from those not considering particle rotation. According to the simulation results, particle rotation enhances particle aggregation and decreases the bed expansion height, particle axial velocity and total granular temperature. The energy dissipation that is produced by particle rotation constitutes approximately 25% of the total energy dissipation in a liquid-solid system. In addition, two factors that affect particle rotation are explored by changing the tangential restitution coefficient of the particles and the liquid velocity. The simulation results demonstrate that the particle rotation effect is the most significant at β = −0.2, and the particle rotation is enhanced with the increase in the liquid velocity.

Hydrodynamic Characterization of a Shallow Rectangular Spouted Bed Using Bed Pressure Signals and Image Processing Methods

To support the design of spouted bed reactors, experiments are performed in a rectangular spouted bed to measure the peak pressure drop (ΔPmax) and the internal and external spouting velocities (Uis and Ues). Four particle types spanning under Geldart D and B are used. Uis and Ues are measured from bed pressure drop and expansion ratio profiles, respectively, with the Ues/Uis ratio of each particle type obtained. Correlations predicting the ΔPmax of Geldart D and B particles are developed by reviewing published correlations and investigating the nozzle effect. Good prediction is achieved with a slope of 0.997 and an adjusted R2 of 0.998 in a 95% confidence interval. Ues is predicted through correlations developed by adding effects of dp/Di and H0 in the Mathur–Gishler equation. The calculated Ues agrees well with the experimental data, achieving a slope of 0.998 and an adjusted R2 of 0.998 in a 95% confidence interval.

Effects of liquid property on onset velocity of circulating fluidization in liquid-solid systems: A CFD-DEM simulation

Knowledge on regime transition from conventional to circulating fluidization is important to scale-up and operation of liquid-solid fluidized systems in industrial applications. Previous experimental studies reported that the onset velocity measured by bed empty time test is pertinent to the physical properties of particle and liquid, and independent of solid inventory, bed geometry, and configuration. The effect of liquid properties is, however, not clear yet since tap water is usually used as the working fluid in laboratory test for convenience. To address this problem, a Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) model is applied to numerically measure the onset velocity of particles in different liquid media. The model is first validated in terms of the experimental data of bed expansion in literature. Then several kinds of particles and three kinds of liquid media of different densities and viscosities are further simulated. We find that the Reynolds number based on onset velocity and Archimedes number follows a power-law relationship. With the decrease of Archimedes number, the discrepancy of Reynolds number based on onset velocity and that on particle terminal velocity becomes highly significant. The ratio of the onset velocity to particle terminal velocity for various particles in one liquid medium is not a constant, and instead dependent on both the particle and liquid properties.

Impact of eelgrass bed recovery and expansion on phytoplankton growth through nutrient competition

Eelgrass beds are highly productive and support diverse faunal assemblages; they also take in nutrients from the water and prevent excessive phytoplankton growth in eutrophic coastal waters through the reduction of available nutrients. Despite its importance, the global distribution of eelgrass has declined worldwide. In eutrophic areas with high chlorophyll a (Chl.a) concentrations, natural recovery of eelgrass beds after eutrophication is possible. To facilitate this, sufficient water clarity can be reached after a large enough decrease in phytoplankton concentration. In this study, we proposed a novel indicator for the maximum possible Secchi depth (MPSD), defined as the Secchi depth when the Chl.a concentration is equal to a reference Chl.a concentration. We applied the MPSD to evaluate water clarity improvements through the reduction of terrigenous anthropogenic nutrient loading. We found that phytoplankton did not control water clarity in the study area, which was instead controlled by background factors. Therefore, improvements in water clarity would not be expected after reducing terrigenous anthropogenic nutrient loading. The habitat of Zostera marina is determined by light availability, so we investigated a potential area with ≥20% surface irradiance and Z. marina existed in 27% of it (100 of 373 ha). The maximum further recovery of eelgrass by Secchi depth improvements to the MPSD was estimated at 36 ha. The impact of eelgrass recovery and expansion on phytoplankton growth from May to September was evaluated by a mathematical model under two scenarios: the current eelgrass distribution (100 ha) and potential maximum eelgrass distribution (373 ha). A Chl.a decrease of 1.0–3.0 μg l−1 from 4.0 to 7.0 μg l−1 was achieved in an area from May to July, and the improvement decreased with time. These evaluation methods and findings could help us gain a better understanding of the nutrient management in seagrass-vegetated semi-enclosed seas subjected to anthropogenic nutrient input.

Electrical Conductivity for Monitoring the Expansion of the Support Material in an Anaerobic Biofilm Reactor

This article describes the use of the electrical conductivity for measuring bed expansion in a continuous anaerobic biofilm reactor in order to prevent the exit of support material from the reactor with the consequent loss of biomass. The substrate used for the tests is obtained from a two-stage anaerobic digestion (AD) process at the pilot scale that treats the liquid fraction of fruit and vegetable waste (FVW). Tests were performed with the raw substrate before anaerobic treatment (S1), the effluent from the hydrolysis reactor (S2), and the effluent from the methanogenic reactor (S3) to evaluate its effect on the electrical conductivity values and its interaction with colonized support material. The tests were carried out in a 32 L anaerobic inverse fluidized bed reactor (IFBR), which was inoculated with colonized support material and using two industrial electrodes at different column positions. The results with the previously digested samples (S2 and S3) were satisfactory to detect the presence of support material at the points where the electrodes were placed since the electrical conductivity values showed significant changes of up to 0.5 V, while with substrate S1 no significant voltage differences were appreciated. These results demonstrate that electrical conductivity can be used as an economic and simple mean for monitoring the support material expansion in order to avoid over expansion in the IFBR. It was also demonstrated that the conditions of the substrate in the methanogenic stage (pH and presence of volatile fatty acids) do not affect the operation of the electrical conductivity detection system.

Methodology for hydraulic characterisation of the sand filter backwashing processes used in micro irrigation

The correct operation of the backwashing process in sand filters used in micro irrigation determines directly the effectiveness of the subsequent filtration processes, and consequently the micro irrigation systems maintenance. As backwashing involves the filter bed expansion, the current sand filter design makes it impossible to measure the process. In this sense, this work aims to present a hydraulic characterization methodology of the backwashing process of sand filters used in micro irrigation, evaluating the influence of the sand particle size, the filter bed height, and the sand filter design. The proposed methodology can assist manufacturers in gathering equipment operating information, aiming at its presentation in the product catalogs.•This method article discusses a method of hydraulic evaluation of the backwashing process of sand filters used in micro irrigation.•The method can assist sand filter manufacturers in the correct definition of the equipment's operating parameters.•The method shows the effectiveness of using the filter media pressure loss evaluation in the indirect definition of the minimum fluidisation velocity.