Fluidization Performance Research Articles

Studies on the fluidization performance of a novel fluidized bed reactor for iron ore suspension roasting

A U-type reduction chamber (URC) is developed as the key component of the novel iron ore suspension roaster. It consists of a fluidization chamber (FC) and a supply chamber (SC), and functions dually as sealing valve and reduction chamber. This roaster has been applied successfully to iron ore reduction roasting, while only limited information is available on its working mechanism. The fluid dynamic behavior of solid particles within URC and effects of operating parameters, i.e., the fluidizing air velocity, aeration air velocity and delivery rate, on its performance were investigated in this study. Simulation experiments on the fluid behavior of feed ores were conducted in a cold operating URC apparatus using alumina particles with an average size of 147 μm. It was found that the feeding particles descend in moving-bed mode in the supply chamber, while the particles move upwards in fluidization mode in the FC under suitable operating conditions. The differential pressure fluctuation reaches the maximum at the middle region of the FC, indicating vigorous gas-solid interactions at this area. The solids holdup presents an “S” shape distribution along the height of the FC. The average solids holdup and axial nonuniformity index range from 0.35 to 0.50 and from 0.10 to 0.40, respectively, which are relatively higher than those found in conventional fluidized bed reactors, ensuring better gas-solids contacting and mixing and promotion of reduction performance. In addition, the solids height in the SC could self-adjust to maintain pressure balance in the URC system under various operating conditions, and the pressure difference produced by solids at a certain height in the SC is the main driving force to keep normal flow of solid particles. The information obtained from this study could be helpful, especially for the regulation and control of industrial iron ore suspension roasting.

Design Impact on Airflow Patterns in Fluidization Units

AbstractThe airflow behavior in a fluidization unit was integrally studied by means of experimental work and computational fluid dynamics simulation. The computational domain included the gas inlet pipe, plenum, perforated plate, fluidization chamber, and air outlet pipe. Different scenarios were simulated to allow distinguishing the best way to represent perforated‐plate distributors and elucidate the impact of the grid design on the fluidization performance. The simulated pressure drop across the distributor and the plenum flow pattern were in concordance with the experimental data. It was found that the distance between the peripheral holes and walls has a great impact on the airflow downstream the distributor.

Moisture transfer of wet coal and its effect on fluidization behavior in a gas–solid separation bed

The characteristics of gas–solid fluidized beds, which are often applied for the separation of minerals, are affected by the moisture carried by wet coal. 3D X-Ray Microanalyser (3D-XRM) and electrical capacitance tomography (ECT) were used to monitor the moisture transfer process of wet coal, as well as the structure and distribution of agglomerates formed in the bed. The fluidization performance of the bed was then studied by a high-speed camera system and pressure drop measurement. The moisture in the wet coal was found to be mainly in the form of free moisture or external moisture on the coal surface. The free moisture mainly formed agglomerates of magnetite, whereas the external moisture caused magnetite to adhere to the surface of raw coal. The agglutinating value of wet coal is mainly affected by external moisture and size fraction, but has little correlation with coal density. The tendency of the formed agglomerate content can be divided into three stages: (i) When the external moisture is 1%, no agglomerates appear in the bed; (ii) When the external moisture reaches 2%, agglomerates are present in the form of magnetite adhering to the coal surface; (iii) When the external moisture exceeds 3%, magnetite adhered to the coal surface is dominant for the agglomerates. Excess moisture will cause the magnetite itself to agglomerate and participate in the internal particle circulation in the bed. At the same time, the moisture content plays a crucial role in the fluidization behavior of the bed. As the moisture content increases, the fluidization behavior of the bed begins to transition from group B to An under low moisture content (<0.25%), and eventually to group C for high moisture (>0.75%).

Pressure fluctuations analysis on the powder fluidization performance at different pressure

Powder propellant feeding system is the key part of powder engine, and the powder fluidization process is quite complex due to the comprehensive effects of intake type, piston and compressible dense gas-solid flow in tank. In order to explore the regimes and fluidization characteristics at high pressure, in this paper, visualization technique with pressure transducer are applied, and the pressure signals have been analyzed by using standard deviation and wavelet transform methods. It is found that in powder tank the fluidization regime will be changed with the increase of pressure: from partial powder fluctuation at low pressure (0.4 MPa) to steady gas-solid interface at high pressure (2.5 MPa), and the regime phenomenon can be explained roughly by standard deviation analysis of pressure signals. Meanwhile, the flow representations of pressure sub-signals were redistricted through wavelet energy method based on ten-level decomposition: the approximation sub-signal a10 (0–4.88 Hz) represents the fluidized gas intake, sub-signals d8–d10 (19.53–39.0625 Hz) represent the powder flow structure changing, gas-solid interaction is represented by d6–d7(39.0625–156.25.Hz), and sub-signals d1–d5 (156.25–5000 Hz) can be used for gas turbulence flow representation. Where gas turbulence and powder fluctuation were determined as the main contributions to pressure fluctuation in the tank. Otherwise, the wavelet energies of sub-signals except for approximation decrease with pressure increase, but there exist large differences for that with the increase of particle mean diameter with different leading force, and the easier entrainment for different size powder, the slighter effects of gas turbulence and gas-solid interaction.

Research of Filling Ratio and Fluidization Performance of Dense-Packing Aluminum Powder

Based on the granule packing theory, grading vibrating filling experiments have been carried out for aluminum powder with different particle sizes. The effects of the several factors on the dense filling ratio of aluminum powder, such as filling craft, vibration time and grading parameter, have been discussed. The distribution uniformity of particle size and fluidization performance of the dense-packing aluminum powder have been detected and analyzed. The results show that the powder filling ratio can be improved greatly by performing the batch packing, stirring and vibrating on powder. The initial vibration can improve the powder filling ratio obviously, but the ascension is not obvious with the increasing of vibration time. The selection of grading parameter should ensure that the small particles can fill in the gaps among large particles. The filling ratio as high as 73.02% has been obtained under the grading parameterm100 μm:m15μm:m1μm=6.89:2.97:1. The testing results show that the size uniformity of aluminum powder obtained by this filling craft is good at the same height, but need to be improved at different heights. The fluidization performance of dense-packing aluminum is good, and the accuracy of powder supply reaches 3.6%, which can meet the requirement of powder supply in powder rocket engine.

Aggregation and fragmentation of agglomerates in a fluidized bed of mixed nanoparticles by adding FCC coarse particles

In this study, the influence of fluid cracking catalyst (FCC) on the fluidization behavior of ZnO-CuO binary nanoparticles was systematically investigated by varying FCC size. High-speed camera was employed to analyze the collision and fragmentation process of agglomerates with adding FCC coarse particles. It can be found from photographs by the camera that fluidization performance improved by the agglomerate variation that is bound to be shaped a compact and spherical structure. Furthermore, the result of agglomeration composition analysis showed that uniform mixing of nanoparticles remarkably affected the fluidization behavior of ZnO-CuO binary system. Finally, the improvement of fluidization performance can be justified by the analysis of inter-cohesive force between the two agglomerates with sharp reduction of the newly-formed agglomerates.

Numerical Investigation on the Two Phase Flow Behaviors in Supercritical Water Fluidized Bed with Swirling Flow Distributor

ABSTRACTSupercritical water fluidized bed reactor is a promising in the clean and efficient conversion of coal, and the distributor is one of the key component for the heat and mass transfer enhancement. However, the optimization study for the distributor in supercritical water fluidized bed reactor has been seldom conducted due to the special thermal properties of supercritical water. In this work, the swirling flow distributor was designed for its optimization for heat and mass transfer inside a supercritical water fluidized bed reactor. The swirling flow can be generated by the concentric circle or triangle type hole distribution in distributor with 0 or 45° intersection angle between the fluid inlet velocity direction and the distributor plane. The computational particle fluid dynamics (SCWFB) method, which has quick calculating speed and high accuracy, was used in this work to study the particle-fluid two-phase flow behaviors inside SCWFB with swirling flow distributors. Investigations were made to reveal the influence of the hole distribution type and intersection angle on the bed pressure drop and particle volume fraction characteristics. The results showed that the triangle type distributor with 45° intersection angle has the best fluidization performance. The conclusions drawn may has potential application for continuous and stable operation of supercritical water fluidized bed reactor for coal gasification.

Pulsation-assisted fluidized bed for the fluidization of easily agglomerated particles with wide size distributions

Fluidization of particles with a high moisture content and wide size distribution is difficult. In this study, pulsation-assisted flow (PAF) was used to enhance the fluidization of wet particles with a wide size distribution. The combination of pulsed and steady flow increased the particle-mixing rate and broke the liquid bridge between solid particles, which prevented particle agglomeration. PAF enhanced the fluidization performance by increasing the separation rate of large particles, thus narrowing the size distribution in the fluidized bed. The effect of PAF on the fluidization performance was also investigated using a newly developed fluidization model, which was verified by comparison with experimental results. The model was used to investigate the relationship between bubble size and pulsed flow frequency, as well as the effect of pulsed flow frequency on particle agglomeration. The model could also predict the optimal pulsed flow frequency for fluidization of wet particles.

The influence of surface hydrophobicity in fluidization of ultrafine Al2O3 particles

A new approach is hereby presented to study the influence of surface properties on ultrafine alumina (Al2O3) particles towards a fluidized performance by changing the ultrafine particles (Al2O3) surface hydrophobic degree. A number of variables that affects fluidization performance of ultrafine particles (Al2O3), including hydrophobicity has been studied. The minimum full fluidization velocities (Umff), average bed pressure drop (ΔPa), standard deviation in pressure drop (σp) and so on, has been found to depend on the hydrophobic degree, which is a function of the ultrafine particles (Al2O3) surface properties. After treatment of the ultrafine particles (Al2O3) with a surfactant, the liquid-solid contact angle on the ultrafine particles (Al2O3) raises, thus changing the interaction between the ultrafine particles (Al2O3) and also between the ultrafine particles (Al2O3) with the micro-fluidized bed wall surface. Furthermore, some changes in important parameters such as particle size (simple agglomerate size), bulk density, flow function plots, maximum wall friction angle, BET parameters and so on were also evaluated. The fluidization of ultrafine particles is attractive, if the interaction forces between the ultrafine particles (Al2O3) and also between the ultrafine particles (Al2O3) with the micro-fluidized bed wall surface can be artificially controlled. Moreover, it is possible to achieve a better fluidization performance on the ultrafine particles (Al2O3). However, more investigation is required to improve the fluidization performance of the ultrafine particles.

DEM-CFD analysis of contact electrification and electrostatic interactions during fluidization

Contact electrification and electrostatic interactions often occur in the fluidization process, which can significantly influence the dynamic behaviour of particles and the fluidization performance. In this study, a discrete element method coupled with computational fluid dynamics (DEM-CFD) is developed by implementing contact electrification and electrostatic interaction models and the combined effects of contact electrification and electrostatic interaction on fluidization are analysed. It is found that the charge of the particle system increases with the superficial gas velocity. Particles of different material properties (especially work function) can be bi-charged and form agglomerates. At low superficial gas velocities, the particle bed cannot be fully fluidized and the pressure drop tends to be stable rather than fluctuating as the gas flows through the micro-channels of the formed agglomerates. However, at high superficial gas velocities, the agglomerates can break, inducing strong fluctuation of the pressure drop. This implies that the electrostatic phenomena and fluidization behaviour can mutually influence each other during the process.

Energy-efficient fluidized bed drying of low-rank coal

An energy-saving and economical process was developed for drying low-rank coal using steam as the drying medium. Based on simulation tests, the energy consumption of the process was found to be nearly 30% lower than that of vapor recompression drying. The proposed process involves the removal of the freezable water in the coal in an exergy recuperative module, while the non-freezable water is removed in a heat integration module. During the removal of the freezable water, the evaporated water is compressed to a low pressure and recycled to the fluidized bed dryer for heat exchange with the incoming coal to minimize exergy destruction. Conversely, medium-pressure steam extracted from a steam turbine is used as the heat source for the removal of the non-freezable water. No compressor was used in the process which significantly reduced the capital cost. Moreover, technical feasibility has been verified through investigating the fluidization performance of the low-rank coal particles in the fluidized bed dryer during the proposed process, particularly to determine the effect of the increased heat exchange tubes on the fluidization performance.

Effect of agitation on the characteristics of air dense medium fluidization

In order to study the effect of agitation on the characteristics of air dense medium fluidization, we designed and constructed an agitation device. Analyses were then conducted on the fluidization characteristics curves, the bed density stability and the average bubble rise velocity Ua under different agitation conditions. The results indicated that a lower bed pressure drop (without considering lower gas velocity in a fixed bed stage) and higher minimum fluidized velocity are achieved with increasing agitation speed. The height d (distance between the lower blades and air distribution plate) at which the agitation paddle was located had a considerable effect on the stability of the bed density at 9.36cm/s<U<10.70cm/s. The higher the value of d, the better the stability, and the standard deviation of the bed density fluctuation σ dropped to 0.0364g/cm3 at the ideal condition of d=40mm. The agitation speed also had a significant influence on the fluidization performance, and σ was only 0.0286g/cm3 at an agitation speed of N=75r/min. The average bubble rise velocity decreased significantly with increasing agitation speed under the operating condition of 1.50cm/s<U–Umf<3.50cm/s. This shows that appropriate agitation contributes to a significant improvement in the fluidization quality in a fluidized bed, and enhances the separation performance of a fluidized bed.

Transient reacting flow simulation of spouted fluidized bed for coal-direct chemical looping combustion with different Fe-based oxygen carriers

Coal-direct chemical-looping combustion (CD-CLC) is a next generation combustion technology that shows great promise as a solution for the need of high-efficiency low-cost carbon capture from fossil fueled power plants. To realize this technology on an industrial scale, the development of high-fidelity simulations is a necessary step to develop a thorough understanding of the CLC process. In this paper, simulations of multiphase flow in a CD-CLC process with chemical reactions are performed using the ANSYS Fluent CFD software. Discrete Element Method (DEM) provides the means for tracking the motion of individual metal oxide particles in the CD-CLC system as they react with the fuel and combine with CFD for capturing the solid–gas multiphase hydrodynamics. The overall results of the coupled CFD/DEM simulations using Fe-based oxygen carriers reacting with gaseous CH4 demonstrate that chemical reactions have been successfully incorporated into the CFD/DEM approach. The simulations show a strong dependence of the fluidization performance of the fuel reactor on the density of bed material and provide important insight into selection of a right oxygen carrier for the enhanced performance. This work provides the foundation for future simulations of CD-CLC systems using solid coal as fuel, which will be crucial for successful deployment of CD-CLC technology from the laboratory scale to pilot and industrial scale projects.

Innovative Steam Drying of Empty Fruit Bunch with High Energy Efficiency

Empty fruit bunch (EFB) is one of the solid wastes from crude palm oil mills and has the lowest value for utilization compared to other solid wastes. To achieve an efficient utilization of EFB, drying is considered the first crucial process due to the high moisture content of EFB. In this study, EFB drying based on exergy recovery is proposed to achieve high energy efficiency. A fluidized bed is adopted as the main dryer. The proposed model is evaluated in terms of energy efficiency, especially regarding the influence of target moisture content and fluidization velocity. Up to 92% of the energy involved in the drying process can be recirculated. The total energy consumption for drying decreases as the target moisture content decreases, though there is no significant impact of fluidization velocity to total energy consumption. In addition, the required total length of the heat transfer tubes immersed inside the fluidized bed dryer is calculated because it relates to fluidization performance and economic issues. Lower target moisture content results in a longer heat transfer tube, and higher fluidization velocity leads to a shorter heat transfer tube.

Fluidized countercurrent solvent extraction of oil pollutants from contaminated soil. Part 1: Fluid mechanics

Liquid–solid countercurrent solvent extraction is a potential application way for the removal of oil pollutant from contaminated soil. This study focuses primarily on the fluidization performance of liquid–solid two-phase flow in an extraction column (2.1m×50mm diameter), with the solvent and solid flow rates ranging from 10 to 800Lh−1 and from 8 to 107kgh−1, respectively. Several key hydrodynamic parameters, including pressure drop, solid holdup, superficial velocity of the solvent and solid, and dimensionless slip velocity, were investigated experimentally. At a given solid flow rate, a uniform axial distribution of solid holdup was observed at low solvent flow rate, whereas the axial solid holdup gradient increased with the solvent flow rate. The appearance of a solid holdup gradient was mainly attributed to the presence of small particles. An operating curve for the soil remediation by countercurrent solvent extraction was obtained according to the critical flow rate of the solvent and solid for predicting the occurrence of flooding and the appearance of the solid holdup gradient.

Novel fluidized bed dryer for biomass drying

Biomass drying is performed mainly in rotary dryers, which occupy a large footprint. To explore the efficient drying of biomass, a fluidized bed dryer was proposed. Good circulation of biomass particles could be established in the fluidized bed without the use of inert particle or mechanical aids. The initial moisture content of the input sawdust affected its fluidization performance. For the drying of sawdust of high-moisture content, the fluidization behavior could be divided into three stages: partial fluidization, full fluidization with increasing drying rate, and full fluidization with decreasing drying rate. A high drying rate could be achieved because of the fast mass and heat transfer rate in the fluidized bed. The fluidized bed dryer has a drying performance similar to the binary mixture fluidized bed dryer but more compact, and requires no separation of dried biomass particles from the inert bed particles.

Fluidization Characteristics of the Dense Gas-Solid Fluidized Bed Separator Based on the Mixed-Medium Solids of Magnetite and Paigeite Powder

Fluidization characteristics of the mixed magnetite and paigeite powder were studied by the combination approach of numerical simulation and experimental verification to optimize the design of the medium solids used in the dense gas-solid fluidized bed separator (DGSFBS). The experimental results showed that the favorable fluidization performance could be achieved with the weight proportion of paigeite powder in the mixture 25% ≤ α ≤ 35%, while the relative deviation in the bed density should be Δρ ≤ 0.025 g/cm3. The corresponding simulation results were obtained by selecting suitable mathematical models and parameters. It also indicated that the fluidized bed with mixed solids could provide a good fluidization performance and stable density distribution. The laboratory-scale DGSFBS was used to conduct the separation experiments on raw coal with size range of 13–6 mm and ash content of 33.43%. With the parameter α = 30%, the experiment resulted in the coal ash content being reduced from 33.43% to 11.63% with a probable error, E P of 0.07 and a recovery efficiency of 98.59%. Utilization of either magnetite or paigeite powder alone was not effective; however, fluidization performance and separation efficiency of DGSFBS improved with the utilization of mixed solids.

Homogeneous Fluidization of Geldart D Particles in a Gas–Solid Fluidized Bed with a Frame Impeller

The influence of agitation of a frame impeller on the fluidization performance of Geldart D particles is experimentally and numerically studied in a gas–solid stirred fluidized bed, using a three-dimensional (3D) unsteady computational fluid dynamics (CFD) simulation. The bed pressure drops obtained from simulations are in reasonable agreement with those measured with pressure transducers, which validates the CFD models. The experimental results of the pressure fluctuation and the simulated ones of the solid volume fraction distribution show that Geldart D particles can perform homogeneous fluidization in the presence of the impeller. The homogeneous fluidization regime expands as the minimum bubbling velocity increases with the agitation speed while the minimum fluidizing velocity remains unaffected. In addition, the uniformity of particle velocities that are distributed in the entire fluidized bed is also improved by the agitation of the frame impeller.

Effect of agitation on the fluidization behavior of a gas–solid fluidized bed with a frame impeller

The effect of agitation on the fluidization performance of a gas–solid fluidized bed with a frame impeller is experimentally and numerically investigated. A 3‐D unsteady computational fluid dynamics method is used, combining a two‐fluid model and the kinetic theory of granular flow. The rotation of the impeller is implemented with a multiple reference frame method. The numerical model is validated using experimental data of the bed pressure drop and pressure fluctuation. Although the minimum fluidizing velocity and bed pressure drop are independent of the impeller agitation, a sufficiently high agitation speed yields higher fluidization performance with reduced bubble diameters and internal circulations of particles. The fluidized bed can be divided into three zones: inlet zone where the gas distribution plays a major role, agitated fluidization zone where the impeller agitation has a positive effect on fluidization, and free fluidization zone where the impeller agitation has no effect on fluidization. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1066–1074, 2013

Experimental Study on Fluidization Characteristics of Gas Quenching Steel Slag

In order to study the application of fluidized bed process for the gas quenching steel slag(GQSS) slag-iron separation, according to the principles of fluidized bed material separation, based on the all GQSS, this paper researches the influence law of fluidization characteristics and the fluidization performance of GQSS after adding 20% (calculated by volume) iron grains. The experiment uses single hood fluidized bed as experiment device, studies the GQSS and iron grains of critical fluidization and slugging fluidization of other characteristics in the fluidization process, and determinates the packing density in interior and exterior of the tube. The results show that: when the material is all GQSS, the appropriate fluidization thickness of material layer is 300~400mm ; after adding 20% iron grains in the tube, the appropriate fluidization thickness of material layer is 350~400mm. The results of this paper on GQSS slag-iron separation have important theoretical significance.