Bed Pressure Drop Research Articles

Fluidization and separation characteristics of a gas–solid separation fluidized bed in the presence of an acoustic field

The bed fluidization characteristics, such as pressure drop, minimum fluidization gas velocity, density, and voidage, play a vital role in understanding the hydrodynamic behavior of fluidization technologies. In this work, the variation in the bed pressure drop was analyzed in presence and absence of an acoustic field. Meanwhile, the minimum fluidization gas velocity was investigated for five different fine particle (−0.074 mm) contents as the acoustic source varied between 90 and 150 Hz, and the sound pressure level was within a range of 100–135 dB. The experimental results show that, upon an increase in the fine-grained particle (−0.074 mm) content, the sound frequency and sound pressure level have different effects on the minimum fluidization gas velocity. The introduction of an acoustic wave can effectively ensure the stability of the bed density, thus improving the separation performance of a gas–solid separation fluidized bed, with a lower probable error E.

Determining the Parameters of the Fluid Layer with a Rigid Mobile Nozzle

Hydrodynamic problems of a three-phase fluidized bed are considered. The main attention is paid to experimental studies into the process of cooling industrial circulating water in a three-phase layer. An experimental setup was developed and assembled, and its brief description and operating principle are given. Adjustment experiments and experiments with a two-phase fluidized bed were carried out, the main task of which was to determine the dependence on the air velocity in the apparatus of the hydraulic resistance of a dry grate without a nozzle. A series of experiments is described that made it possible to establish the optimal cooling mode for circulating water in an apparatus with a three-phase fluidized bed. The experiment was carried out at both constant and variable irrigation density, and the experiments were repeated at different air velocities. The following parameters of the three-phase fluidized bed were recorded: hydraulic resistance, the rate of onset of fluidization, the rate of entrainment, and the height of the dynamic bed. The results of experimental studies into the fluidization rate and entrainment rate at various ball nozzles and the dependence of the dynamic height of a three-phase fluidized bed on the rate and density of irrigation are presented. Experimental data have been obtained on the pressure drop in a three-phase fluidized bed depending on the air velocity, the rate of the beginning of fluidization of the irrigated bed of the packing, and the rate of flooding of the three-phase fluidized bed as a function of the irrigation density. The analysis of hydrodynamic and thermal processes occurring in a three-phase fluidized bed is carried out, and the main technological parameters for the optimal operation of installations with the specified bed are obtained in relation to solving the problem of cooling the circulating water. The dependence of the expansion of a three-phase fluidized bed on air velocity and irrigation density has been investigated. On the basis of the performed experimental studies, empirical formulas for calculations are derived.

Particle-resolved CFD simulation of fixed bed pressure drop at moderate to high Reynolds number

Particle-resolved computational fluid dynamics simulations of flow and pressure drop in fixed beds of spheres give poor accuracy at higher Reynolds number (Re) under turbulent conditions. The influence of meshing is investigated for two cases, a face centered cubic packing with no wall effects, and a narrow bed of tube-to-particle diameter ratio three with strong wall effects. Local approaches to meshing at contact points were compared, using both surface flattening (caps) and bridging between spheres. Accurate results for pressure drop at moderate to high Re > 1000 required computationally expensive fine uniform meshes, however at highest Re pressure drop appeared to be low. The use of boundary adaption improved results with less expensive meshes. The aspect ratio of surface prisms and the sizes of the bridges used at contact points had strong effects. Velocity profiles were much less sensitive to the mesh refinement and could be obtained at reasonable cost.

Fluidization of biomass: a correlation to assess the minimum fluidization velocity considering the influence of the sphericity factor

This paper deals with the influence of different definitions for evaluating the sphericity factor on the prediction of minimum fluidization velocity (U mf) of different agro-industrial/forestry biomass residues and sand. Three biowastes (sawdust, grape marc, and grape stalk) and sand were characterized by sieving, and sphericity was calculated using images obtained by scanning electron microscopy (SEM). Two particle size populations (with mean diameters and density corresponding to B and D Geldart groups) were adopted for each biomass. As for sand, particles with a mean diameter of 0.33 mm were used. Tests were carried out in a lab-scale fluidized bed. Bed pressure drop was measured as a function of the superficial velocity of air at two different initial bed heights, for each type of biomass and mixtures with sand. Ratios of 0.50 and 0.75 (v/v) were used for mixtures. For all cases, U mf values were calculated experimentally and were compared against predicted values obtained from Ergun's equation and other correlations. It was found that the methodology adopted for determining sphericity significantly influences the obtained value of U mf. The lowest relative error between predicted and experimental U mf values was obtained using Riley’s sphericity method. Finally, a new correlation for U mf was proposed.

Understanding pressure changes in smouldering thermal porous media reactors

The use of thermal porous media reactors for environmental applications is growing rapidly. Understanding the pressures increases inherent in such systems is central to their success. Numerical modelling of thermal processes in porous media, supported by experiments, quantifies and explains the pressure increases occurring during gas injection into smouldering treatment systems. Air flux and pressure gradient are revealed to be linked by the pneumatic conductivity of the porous bed at two scales. Locally, air density, viscosity, and velocity are coupled to temperature. However, the air pressure gradient increases globally due to a global reduction in pneumatic conductivity. Finally, a new, simple method to estimate the maximum bed pressure drop for thermal porous media reactors is presented. Overall, this work provides the first quantitative analysis of these local and global phenomena in such systems and provides a simple design tool for engineers.

Preliminary study for the suitability of eucalyptus chips and coal for combustion in a fluidized bed reactor

The combustion with fluidized bed reactors has as main advantages the best energy utilization of combustible materials and a lower generation of pollutants. The fluidization success depends on the characteristics of the particles that compose the bed. This research aimed to perform a preliminary evaluation and characterization of the energy potential and the fluidization curves in fluidized beds formed by binary mixtures of eucalyptus chips + sand and mineral coal + sand. We tested: 1) physical characterization of solid fuels; 2) chemical characterization of combustible materials; 3) thermogravimetric analysis of fuels; 4) determination of the fluidization curves and minimum fluidization velocity for a polydisperse bed. We observed 19.15 MJ kg-1 of lower calorific value for eucalyptus chips and 10.1 MJ kg-1 for coal. The increase in biomass percentage in mixture caused a pressure drop in bed, indicating the formation of preferred paths and a necessity to increase fluid velocity. The fluidization of coal and Eucalyptus chips can be viable in a bubbling fluid bed process, motivating future theoretical and experimental studies involving the application of this methodology in the development of clean and sustainable technologies.

Numerical investigation of flow stratification behavior of binary particle mixture for high-temperature flue gas filtration on an inclined moving bed

Although the filtration efficiency can be increased because of the use of small-sized particles in granular beds, the bed pressure drop may be increased. This study presents a numerical solution of a moving bed that can facilitate instantaneous separation of binary particles into a top layer of larger particles and a bottom layer of smaller particles during the flow. The particle discrete element method is used to simulate the flow process of binary particles, which is verified by experiments. An index to measure the effect of stratification and the separation degree (SD) are proposed. Results show that SD increases as the particle size ratio and the mass fraction of coarse particles increases. The thickness of the coarse particle layer increases as the mass fraction increases. The surface thickness and segregation are within the optimum when the particle size ratio is 2.5 and the mass fraction of coarse particles is 65%.

Modelling the stochastic nature of porosity in a respirator canister using computational fluid dynamics

AbstractA model has been developed to represent the stochastic nature of the activated carbon bed within a generic chemical biological radiological and nuclear (CBRN) respirator canister. The porous region is subdivided into discrete sections which are assigned a porosity based on their radial position according to a longitudinally‐averaged porosity model, and then perturbed by some amount according to a Gaussian distribution. The porosity model was used in Reynolds‐averaged Navier‐Stokes (RANS) simulations in order to assess the impacts that the choice of section size and the porosity variation would have on the pressure drop and residence time distribution. It was shown for small section sizes that increasing porosity variation would increase pressure drop and minimum residence time in the carbon bed, while decreasing the average residence time. As the section sizes became larger the reverse trend was seen as a greater extent of flow channelling throughout the bed became apparent. For the given domain size, there was an upper limit to the section size, beyond which statistical convergence could not be guaranteed. It was also shown that for section sizes close to the particle diameter, the results would depend only on the ratio of section size to porosity variation, reducing the porosity model to a single parameter. A few selected cases were simulated at higher flow rates, where the previously mentioned trends were seen to persist.

Influence of frictional packing limit on hydrodynamics and performance of gas-solid fluidized beds

The influence of frictional packing limit (FPL) on prediction of hydrodynamics and performance of fluidized bed reactors was studied. Dense gas-solid flows in non-reactive (under isothermal cold and at elevated temperatures) and reactive atmospheres (fluidized bed gasifier) were simulated using Eulerian-Eulerian methodology considering a range of values for FPL. Simulations under cold flow conditions were conducted to establish a range of FPL values that provides physically realistic predictions. It is noticed that bed pressure drop increases with increasing value of FPL when superficial gas velocity (U) is less than or equal to the minimum fluidization velocity. For larger values of U, predicted pressure drop is unaffected by the choice of value of FPL. However, in these cases, the distribution of particles, their velocities and bubbling behavior are significantly affected by FPL. Effect of FPL at elevated temperatures is similar to the one observed at cold flow conditions. It is further noticed that FPL not only affects the predictions on bed hydrodynamics but also has profound influence on reactive flow characteristics such as bed temperature and product gas composition. Sensitivity analysis under cold flow conditions could reveal better predictions when the ratio of FPL to close packing limit is chosen between 0.9 and 0.97.

Experimental study on defluidization behaviours and its influence factors during gas switching fluidization

In this work, an investigation on the fluidization behaviour of solid particles was carried out while the fluidizing agent was switched from one gas to another with an equal volumetric flow. Four different gases, namely helium, nitrogen, argon and carbon dioxide (He, N2, Ar and CO2), were adopted as fluidizing agents, and fluid catalytic cracking (FCC) was used as the experimental material. When changing the gas supply a sharp decrease of the bed pressure drop and significant compression of the emulsion phase are observed, as well as the disappearing of the bubbles and the formation of channels inside the bed. However, these disturbances are temporary, and the initial fluidization conditions can be restored after a certain amount of time. Such behaviour is quantitatively described by measuring the maximum relative decrease of bed pressure drop, the time duration and the intensity of the defluidization phase. The effects of the initial powder bed height, the switching gas velocity and the gas properties are analyzed as well. Finally, a semi-empirical model was developed to predict the defluidization time based on the understanding of this physical process and analyzing the experimental data.

A volatile spray zone model and experimentation in a gas-solid fluidized bed with liquid injection

In a gas-solid fluidized bed, volatile liquid injection results in complex flow behaviors in the spray zone. To characterize the liquid existence forms (droplets and liquid films) and fluidization properties in the volatile spray zone, a mesoscale-theory based volatile spray zone model is developed with the consideration of hydrodynamics, heat transfer, and mass transfer. A new energy-based stability condition is established according to two competition and coordination relationships, consisting of the energy dissipation based on the liquid-solid interface change and suspension and transporting of particles. The modeling results agree well with the experimental bed temperature as well as void fraction data, and show that the variation of liquid existence forms is dependent on the ratio of different energy consumption rates under the stability condition. Moreover, the gas-solid drag coefficient in the volatile spray zone is modified. Simulation results also reasonably describe the bed pressure drop fluctuation and particle velocity distribution.

Experimental and numerical analysis of void structure in random packed beds of spheres

The prediction of the pressure drop of packed beds requires an accurate estimation of the packed-bed porosity as its error propagation multiplies the occurring errors by a factor of about four. For a better understanding of the packed bed's local porosity characteristics, a comprehensive x-ray tomography study was performed investigating and correlating the void structure of packed beds made of smooth, mono-sized spheres in cylindrical confining walls having tube-to-particle diameter ratios λ = 3.0 to 9.0 reinforced by numerically generated packed beds of λ = 1.1 to 9.0. An in-depth analysis of the obtained oscillating void profiles is performed, discussing the locations and heights of porosity extrema. Most importantly, a significant and in parts surprising extrema formation in the tube's center is described, especially present for λ < 6, which is assumed to have a predominant effect on the packed bed's pressure drop.

Effect of particle size and shape on liquid–solid fluidization in a HydroFloat cell

The separation of coarse particles by flotation can be maximized by the support of fluidized bed hydrodynamics. Here, we investigated the effect of particle size and shape on the liquid-solid fluidization in a HydroFloat cell that was developed for the special separation process using CFD results and experimental data. Specifically, a 3D CFD model was developed to study the liquid and aspherical quartz particle flow behaviors in a fluidized bed in the cell. The Eulerian–Eulerian formulation with the RNG k-ε turbulence model was applied for the liquid phase, while the kinetic theory of granular flow was utilized for the particle phase. The Gidaspow with Haider and Levenspiel equations were used for the drag force coupling between the liquid and the aspherical particles. The CFD results agreed with the experimental data for the bed voidage and pressure drop. The CFD model was further applied to investigate the effect of particle size (dS) and particle shape factor (ψ) on the bed expansion, pressure drop, and voidage of the fluidization for Re (particle Reynolds number) < 11.6. The Richardson-Zaki equation was modified to predict the voidage, within 12% of relative errors. The prediction was further improved by our semi-empirical correlation that reduced the errors to 8%. The particle size and shape were also found to significantly affect the time-averaged radial distribution of the axial velocity and volume fraction of the particles, granular temperature, dissipation rate, and viscosity of turbulence. The outcomes of this paper are useful for optimizing the operation of the HydroFloat cell.

Zeolite Heat Storage: Key Parameters from Experimental Results with Binder‐Free NaY

AbstractThe application of heat storage systems in households or the industry is one possibility to optimize the degree of heat utilization and to reduce greenhouse gas emissions. In contrast to established heat storage systems based on water, zeolitic systems reach energy densities of 150–200 kWh m−3 and allow for seasonal storage with almost no heat loss. However, a commercial breakthrough was not yet successful. Given this background, it is the aim of the present study to identify appropriate operational parameters for a zeolite heat storage system in the laboratory and to prepare an upscaling to demonstration scale. To this end, the pressure drop of the zeolite bed, the cycle time, and the optimal process parameters during thermal loading and deloading were determined.

Determination of filter bed structure characteristics and influence on performance of a 3D matrix biofilter in gaseous chlorobenzene treatment

The structure characteristics of filter bed greatly affect biofilter performance. In this study, a three-dimensional (3D) matrix biofilter packed with perlite and high mechanical strength 3D matrix material was established. The structure characteristics of the filter bed and the performance of 3D matrix biofilter and control biofilter (packed with perlite) were investigated. The 3D matrix biofilter presented higher chlorobenzene removal performance and lower bed compaction and pressure drop than the control biofilter. The packing factor, which could be used to represent the resistance when the gas stream passed through the filter bed, of the 3D matrix biofilter (7.59 × 105 m−1) was smaller than that of the control biofilter (1.04 × 106 m−1). Moreover, the specific surface area obtained from the molecular residence time distribution curves in the 3D matrix biofilter was higher (1754.82 ± 35.82 m2/m3) than that in the control biofilter (1474.03 ± 25.52 m2/m3), indicating improvements in mass transfer and performance. The characteristic parameters for mass transfer coefficient estimation in the biofilters were determined based on Onda’s modified correlation. 3D matrix biofilter demonstrated higher mass transfer coefficients than the control biofilter due to its higher specific surface area.

Manganese oxide lanthanum-doped alumina catalyst for application in 95 wt.% hydrogen peroxide thruster

In this study, a manganese oxide lanthanum-doped alumina (MnOx/La/Al2O3) catalyst was employed for application in a 95 wt.% hydrogen peroxide thruster. By employing 95 wt.% hydrogen peroxide rather than the conventional 87.5 wt.% hydrogen peroxide, specific impulse is expected to increase. However, a suitable catalyst is needed for the 95 wt.% hydrogen peroxide. Hence, the MnOx/La/Al2O3 catalyst and its reference catalyst, manganese oxide gamma-alumina (MnOx/γ-Al2O3) catalyst were tested by applying hot-firing tests using a 50 N thruster. The test results were examined in terms of characteristic velocity efficiency, catalyst loss rate, pressure instability, catalyst bed pressure drop, chamber pressure, and catalyst bed temperature. The MnOx/La/Al2O3 catalyst showed an equal characteristic velocity efficiency, six times lower catalyst loss rate, 20% lower increment in pressure instability, and 44% lower increment in catalyst bed pressure drop. Therefore, it is feasible to apply the MnOx/La/Al2O3 catalyst in 95 wt.% hydrogen peroxide thrusters.

Hydrodynamic Properties of High Activated y-Al2O3 in a Fixed Bed Reactor

The high activated γ-Al2O3 hydrodynamic properties in the fixed bed are studied in this paper. The factors of gas velocity and the heights of the bed on the axial bed pressure, bed pressure drop and bed voidage are studied. The results indicated that under the same height of fixed bed, the axial pressure decreased along the bed at the same gas velocity. While the pressure drop increased with the gas velocity and the bed height increased. The pressure drop has a good agreement to the Ergun equation. According to the Ergun equation, the bed voidage is regressed at different height of fixed bed. The results revealed that the bed voidage of high-activated γ-Al2O3 is almost the same in the fixed bed heights of 400 mm, 300mm and 200mm, which is 0.31, 0.32, and 0.32 respectively.

Effect of turbulence modeling on hydrodynamics of a turbulent contact absorber

A computational fluid dynamics (CFD) study is conducted to find a suitable two equation turbulence model for accurate prediction of hydrodynamics of an inhouse turbulence contact absorber (TCA) at high gas and liquid velocities. Based on the multi-fluid Eulerian approach, hydrodynamics of TCA is simulated by incorporating three turbulence models i.e. standard k–ε model, RNG k–ε model and SST k–ω model in ANSYS Fluent®. The solid phase stresses were closed by using the kinetic theory of granular flows (KTGF). TCA hydrodynamics parameters; expanded bed height and bed pressure drop were used to compare the results of this study with experimental data and also with earlier numerical study published with laminar viscous model. It was found that the RNG k–ε model predicted the bed height and pressure drop better than its counterparts. To accurately find the effects of secondary phase turbulence, two RNG k–ε model options i-e. per phase and dispersed were also evaluated. The results show that the “per phase” option of RNG k–ε model produced the expanded bed height and pressure drop in close agreement with available experimental data at similar operating conditions.

Computational and Experimental Study on Pressure Drop in a Fluidised Bed with Different Air Distributor Designs

Fluidised bed combustion (FBC) has been recognised as a suitable technology for converting a wide variety of fuels into energy. In a fluidised bed, the air is passed through a bed of granular solids resting on a distributor plate. Distributor plate plays an essential role as it determines the gas-solid movement and mixing pattern in a fluidised bed. It is believed that the effect of distributor configurations such as variation of free area ratio and air inclination angle through the distributor will affect the operational pressure drop of the fluidised bed. This paper presents an investigation on pressure drop in fluidised bed without the presence of inert materials using different air distributor designs; conventional perforated plate, multi-nozzles, and two newly proposed slotted distributors (45° and 90° inclined slotted distributors). A 3-dimensional Computational Fluid Dynamics (CFD) model is developed and compared with the experimental results. The flow model is based on the incompressible isothermal RNG k-epsilon turbulent model. In the present study, systematic grid-refinement is conducted to make sure that the simulation results are independent of the computational grid size. The non-dimensional wall distance, is examined as a key factor to verify the grid independence by comparing results obtained at different grid resolutions. The multi-nozzles distributor yields higher distributor pressure drop with the averaged maximum value of 749 Pa followed by perforated, 45° and 90° inclined distributors where the maximum pressure drop recorded to be about one-fourth of the value of the multi-nozzles pressure drop. The maximum pressure drop was associated with the higher kinetic head of the inlet air due to the restricted and minimum number of distributor openings and low free area ratio. The results suggested that low-pressure drop operation in a fluidised bed can be achieved with the increase of open area ratio of the distributor.

Fluidized bed CFD using simplified solid-phase coupling.

The performance of a bubbling fluidized bed largely depends on the dynamics of solids. Therefore, it is very important to predict the bubble size and shape for modelling the degree of mixing of solid particles. The complicated non-linear characteristics of a bubbling fluidized bed make it difficult to study and model the hydrodynamic behaviour. Hence, designing of a bubbling fluidized bed is often limited to the calculation of mass balance and estimation of bed pressure drop. The aim of the present work is to evaluate a new simplified multiphase Computational Fluid Dynamics (CFD) approach for studying the hydrodynamics of a gas-solid bubbling fluidized bed. In this work, the viability of a simplified coupling of solid-phase with the gas phase over the traditional multiphase approach has been demonstrated. The available traditional multiphase CFD technique is not suitable for capturing the particulate phase in the dense stagnant regions of fluidized bed. This is because, under the traditional CFD multiphase process, solid phase is treated like a fluid. Shear stress is higher when fluid moves and zero when it is stagnant. In contrast, friction force is maximum when solid particles are stagnant. Therefore, a suitable approach is necessary to model the stagnant particulate phase in the calculation domain. In the present simplified coupling process, mass fluxes for the solid phase are obtained explicitly from the solid phase momentum equation and solid pressure is calculated from the solid phase continuity equation. These solid phase flow parameters are incorporated into the commercial CFD software single-phase gas flow by writing user-defined subroutines. The simplified coupling approach is validated against the available experimental digital images and the traditional CFD modelling results of the fluidized bed. The comparison shows, the available traditional multiphase model predicts less realistic or sometimes unrealistic results while the present numerical model captures more realistic results.