Fluidization Quality Research Articles

Study on Fluidization Characteristics of Magnetically Fluidized Beds for Microfine Particles

The bed pressure drop, minimum fluidized gas velocity, bed density, and bed expansion rate are important parameters characterizing the fluidization characteristics of gas-solid fluidized beds. By analyzing these parameters, the advantages and disadvantages of the fluidization state can be known. In this study, experiments were conducted to study the fluidization characteristics of a gas-solid magnetically fluidized bed for microfine particles by changing the magnetic field strength, magnetic field addition sequence, and static bed height. The experimental results show that when the magnetic field strength increased from 0 KA/m to 5 KA/m, the minimum fluidized gas velocity of particles increased from 4.42 cm/s to 10.32 cm/s, while the bed pressure drop first increased and then decreased. When the magnetic field strength is less than 3.4 KA/m, the microfine particles in the bed are mainly acted on by the airflow; while when the magnetic field strength is greater than 3.4 KA/m, the microfine particles are mainly dominated by the magnetic field. The magnetic field addition sequence affects the fluidization quality of microfine particles. The fluidized bed with ‘adding magnetic field first’ shows a more stable fluidization state than ‘adding magnetic field later’. Increasing of the static bed height reduces the bed expansion rate. The bed expansion rate is up to 112.5% at a static bed height of h0 = 40 mm and H = 5 KA/m. This will broaden the range of density regulation of a single magnetic particle and lay the advantage of gas-solid magnetically fluidized bed for microfine particles in the field of separation of fine coal.

An investigation into the effect of particle size distribution on the fluidization behavior of Group C and Group A particles

Group C particles possess great potential in gas-phase catalytic reactions due to the large specific surface area. This work focuses on the effects of particle size distribution (PSD), average particle diameter, and addition of nano-additive on the flowability and fluidization quality of Group C and Group A powders. Virgin Group C powders are hard to fluidize, but with the so-called nano-modulation, Group C powders exhibit readily detectable minimum fluidization velocity (Umf), high bed expansion and large dense-phase voidage. After nano-modulation, Group C particles with a wider PSD show higher bed expansion, indicating better gas-solid contact. On the other hand, a narrower PSD contributes to better flowability, higher normalized pressure drop, and lower Umf. For Group C particles with the same span, a smaller particle size improves bed expansion. Comparative studies also show that the influence of PSD is more significant for Group C particles than for Group A particles.

Theoretical and experimental insight into the homogeneous expansion of wet particles in a fluidized bed

The presence of liquid in a fluidized bed induces a homogeneous bed expansion at incipient fluidization, which improves the fluidization quality by enhancing the gas-holding capacity of emulsion phase. This paper made an insight into the expansion of wet bed through theoretical and experimental approaches. The bed expansion ratio increases with particle diameter and liquid surface tension, and hardly changes with liquid viscosity due to the absence of viscous term in liquid bridge force. The expansion ends up as the tensile strength of wet bed equals to the shear stress from gas drag force. The superficial gas velocity at this point is the complete fluidization velocity, Ucf. Theoretical calculation shows that Ucf sharply increases then gradually saturates with increasing liquid amount. The tensile strength of wet bed is most sensitive to the superficial gas velocity, followed by the particle diameter. The effect of liquid amount is the smallest. From an optimization perspective, increasing particle diameter and liquid surface tension can enhance the gas-holding capacity of a wet bed during fluidization.

Improvement of Fluidization Quality Using Promoter and Modified Design of Distributor–A Review

Persistent efforts were made by various researchers to improve the quality of gas-solid fluidized bed by means of hindering the bubble formation, avoiding the coalescence of bubbles through bubble breakage, thereby exhibiting a meticulous bed expansion and fluctuation. To conquer these difficulties and to achieve a better fluidization quality use of distributor, turbulence and promoter has been recommended and emerged as an alternative and effective technique. The introduction of promoters performs well in smoothening the fluidization operation in terms of infringement of bubbles, and regulating the bubble size through inhibiting their growth. A better fluidization quality is achieved by various fluidization characteristics such as bed expansion, fluctuation, mixing index and minimum fluidization velocity. Therefore, various researchers investigated the usage of different types of promoters and distributors and recommended that by using a suitably designed promoter and distributor possess an improved fluidization quality with marginal fabrication cost, however the operational cost remains unchanged. Most of the literature studies are dealt with the qualitative effect of the usage of promoters and distributors in a gas-solid fluidized bed though investigation of various hydrodynamics characteristics viz. bed expansion ratio, bed fluctuation ratio, bed pressure drop ratio.

Polypropylene Composites Reinforced by Nonmetallic from Waste Printed Circuit Boards Using Spout-Fluid Bed Coating with PP Particles Enhance Fluidization

Nonmetallic materials recycled from waste printed circuit boards (N-WPCBs) were modified by coating KH-550 in a spout-fluid bed. To improve the effect of the modification, PP particles were used to enhance the fluidization quality of the N-WPCB particles in the coating modification. Then, the modified N-WPCBs were used as fillers to fabricate PP/N-WPCB composites. The method of coating in a spout-fluid bed with PP particles enhanced fluidization and showed the best modification effect compared to other coating methods. The FT-IR and SEM results demonstrated that interfacial bonding between N-WPCBs and PP could be enhanced by modified N-WPCBs, which improved the mechanical properties of the composites. When the mass ratio of PP to N-WPCBs is 100:75 and the dose of KH-550 is 4 phr, the flexural strength, tensile strength, and impact strength of the composites increase by 16.60%, 23.22%, and 23.64%, respectively. This would realize the high-value utilization of N-WPCBs with coating modification in the spout-fluid bed.

Hydrodynamic behaviors of a spouted fluidized bed with a conical distributor and auxiliary inlets for the production of polysilicon with wide-size-distribution particles

In order to improve the fluidization quality of wide-size-distribution (WSD) particles in a spouted bed reactor for the production of polysilicon, a conical distributor with one central gas inlet and six auxiliary inlets was designed and applied in a cold-model reactor to form a spouted fluidized bed. The effects of the central and auxiliary gas velocities on the solid holdup were studied in the gas distributor region. The hydrodynamic behaviors inside the conical distributor were analyzed by pressure fluctuation in the time domain (standard deviation) and the frequency domain (power spectral density, PSD). The gas distribution was measured by the gas tracing method. It was found that the auxiliary gas feed significantly re-distributed the solid particles and effectively improved the fluidization quality; the dead zone phenomenon was well suppressed even at a low superficial gas velocity. Based on different flow behaviors, a regime map of fluidization was determined for fixed bed, bubbling bed, spouted bed, and spouted fluidized bed regimes. These results provided guidance for the reactor design because the gas and solid distributions would significantly affect the deposition efficiency of polysilicon.

Steam O2-enriched air gasification of lignite and solid recovered fuel in fluidized bed

Continuous steady-state gasification tests were performed, in which mixtures of lignite and solid recovered fuel (SRF) were fed to a bench-scale facility at atmospheric pressure, loaded with the bottom product of a high-temperature Winkler gasifier as the fluidized bed material. The O2/fuel and steam/fuel ratios were varied from 0.3 to 0.4 and from 0.25 to 0.35, respectively, and the effects of the temperature were examined at different levels (700, 750, and 800 °C). The objective of the experimental campaign was to evaluate the effects of above mentioned operating conditions on the (i) quality of syngas expressed in terms of gas yield (Ygas), cold gas efficiency (ηCG), and carbon conversion (XC); (ii) effectiveness in tar reduction; and (iii) improvement of the H2/CO molar ratio. Characterization analyses (grain-size distribution, scanning electron microscopy and energy-dispersive X-ray spectroscopy) were performed on the materials before and after the tests. Pressure-fluctuation signals were acquired during the tests to monitor the fluidization quality and diagnose the correlated incipient sintering or agglomeration of the bed particles. At 800 °C, the obtained results (Ygas=1.53;ηCG=79%;XC=92%;tar content = 7.35 g/Nm3; H2/CO molar ratio = 0.96) demonstrated the convenient feasibility of gasification with the SRF–lignite mixture as a fuel (SRF/lignite = 0.5 wt/wt) and helped define the operating conditions for future pilot tests aiming for liquid fuel synthesis, although the best results were obtained at 800 °C with SFR/lignite = 0.2 wt/wt (Ygas=1.79;ηCG=93%;XC=102%;tar content = 0.92 g/Nm3; H2/CO molar ratio = 0.84).

Study on the Fluidization Quality Characterization Method and Process Intensification of Fine Coal Separation in a Vibrated Dense Medium Fluidized Bed.

Uniform and stable bed density is the basis of efficient coal separation by a gas–solid dense medium fluidized bed. The traditional air dense medium fluidized bed (ADMFB) is a kind of bubbling bed. By introducing vibration energy, a vibrated dense medium fluidized bed (VDMFB) with uniform and stable bed density can be formed, where the bubble merger is suppressed, the gas–solid contact can is strengthened, and the fluidization quality is also improved. In this paper, the transfer process of vibration energy in a fluidized bed is studied in detail. By calculating the coherence of pressure signals induced by vibration energy and bubbles at different bed heights, the suppression effect of vibration energy on bubble merger is analyzed. The coefficient Rimp to quantitatively evaluate the improvement effect of vibration energy on the fluidization quality is proposed. The differences and incentives of density uniformity and stability in different height bed areas have been clarified under different vibration parameters and gas flow parameters. It is proposed that the optimal separation bed height area of VDMFB is about H = 40–150 mm. The separation effect of the ADMFB and the VDMFB on 1–6 mm fine coal was compared. The results show that, compared with the ADMFB, the VDMFB reduces the separation probable error, E, from 0.134 to 0.083 g/cm3, and the ash content of the clean coal is reduced from 18.83 to 14.97%. The vibration energy significantly improves the fluidization quality of the ADMFB and the separation effect of fine coal.

Effect of agitation on hydrodynamics and separation performance of gas–solid separation fluidized bed

Mechanical agitation was usually applied to improve the fluidization quality of the fluidized bed. This study aimed to explore the effect of agitation on the fluidization characteristics and separation effect of a gas–solid separation fluidized bed. On the basis of the multiple reference frame model, the fluidized bed under mechanical agitation was simulated, where the symmetrical motion pattern of the bed particles was identified. Furthermore, when the agitation speed w was below 75 rpm, the fluidization quality was improved gradually with the lower density fluctuation variance of 0.06 g/cm3. Finally, under the appropriate operating conditions (fluidization number of 1.2, w = 75 rpm), raw coal was separated in a fluidized bed, and the yield of cleaned coal was 41.30% with an ash content of 14.27%. Moreover, the probable error was as low as 0.105 g/cm3, indicating the strong separation performance of the gas–solid separation fluidized bed with an agitator.

Numerical studies of gas-solid flow behaviors and wall wear in a swirling fluidized bed

A swirling gas-solid fluidized bed can effectively improve the fluidization quality and interphase heat transfer via the introduction of tangential gas flow. The Dense Discrete Phase Model (DDPM) is employed to investigate the gas-solid flow behaviors in a swirling gas-solid fluidized bed with the air plenum. In addition, the wall wear and particle mixing behaviors are also examined. The results demonstrate that various operation regimes appear with the increasing superficial velocity. The particles are prone to be centrifugally attached to the wall in the stable swirling regime and accompanied by strong elutriation. The decrease of central body height will reduce the bed pressure drop and swirling velocity. The increase of operation velocity is beneficial to particle mixing behaviors in a swirling bed with a lower central body.

Fluidization dynamic characteristics of carbon nanotube particles in a tapered fluidized bed

These picture shows the energy contribution of micro-, meso- and macro-structures at different operating conditions in the TFB without distributor. Energy contribution of micro-, meso- and macro-structures at different particle size. In this work, a tapered fluidized bed (TFB) without a distributor for fluidizing carbon nanotube (CNT) was applied for improving the dead zone, blockage, and fracture of distributor, which occurred in actual production. Experiments were performed under different superficial gas velocities, static bed heights, CNT agglomerate size, and positions of pressure probe. To obtain multi-perspective and multi-scale understanding of fluidization dynamics of gas–CNT flow in the TFB without a distributor, the standard deviation, skewness, kurtosis, wavelet decompositions and homogeneous index analysis methods were adopted. Some noticeable phenomena were observed. Particle movements including inter-particle, gas–particle and particle–wall dominate dynamic characteristics. The amplitudes of pressure fluctuations of coarse agglomerated multi-walled CNT were more sensitive to the gas velocity than that of fine agglomerated multi-walled CNT. The sensitively of energy contribution of the meso- and macro-structures was that the sensitivity of the measured position was less than the sensitivity of the energy contribution by the changes of particle size, and the sensitivity of the energy contribution by the changes of particle size was less than the energy contribution by the changes of gas velocity. The fluidization quality of coarse agglomerated multi-walled CNT was better than that of fine agglomerated multi-walled CNT, which was verified by the skewness and wavelet analysis.

Fluidization stability vs. powder history of Geldart group C+ particles

Geldart Group C particles with the addition of nanoparticles (Group C+) show a better flowability and fluidization quality. The stability of these Group C+ particles with different nanoparticle concentrations were systematically examined in this work, including the flow properties, the particle size distribution (PSD), and the fluidization behaviors with the fluidizing time. Although the flowability, PSD, and fluidization behaviors for Group C+ particles fluctuated with the fluidizing time, those became more stable after fluidizing for 1–2 h. The increase of the nanoparticle concentration significantly improved the stability of these behaviors for Group C+ particles. Group A particles showed more stable behaviors with the fluidizing time than Group C+ particles, and nanoparticles had a little effect on the stability. In addition, Group C+ particles exhibited much better fluidization behaviors, including higher bed expansion and higher dense phase expansion, than Group A particles, contributing to better gas-solid contact.

Different bubble behaviors in gas-solid fluidized bed of Geldart group A and group C+ particles

A gas-solid fluidized bed reactor composed of Geldart Group C fine powers with the addition of nano-additives (Group C+) has recently been shown to have higher reaction conversion and better contact efficiency than the same reactor composed of Geldart Group A particles due to the increased gas holdup in the dense phase and the increased gas-solid interfacial area. Based on our earlier findings that significantly smaller bubbles were observed in such a Group C+ particle fluidized bed, the bubbling behavior is fully characterized in this work using the bubble position, diameter, rise velocity and residence time. The results indicated that bubbles were smaller in diameter, lower in rise velocity, and had a longer residence time in the Group C+ fluidized bed when compared with the same bed using Geldart Group A particles. All these factors contributed to better fluidization quality and enhanced gas-solid contact, thus improving reaction performance.

Hydrodynamic and separation performance of gas–solid separation fluidized bed with two-size-orifice distributor

The air distributor is an important part of the gas–solid separation fluidized bed, which directly determines the air distribution across the bed base. In this study, numerical simulation and experimental analysis are used together to study the influence of a two-size-orifice distributor on the fluidization quality and separation performance of the fluidized bed. Results show that the bed is prone to channeling when the air distributor contains 6mm orifices, and the values of fluidization parameters of the bed, i.e., pressure drop, voidage, and density stability, increase with decreasing orifice size. Owing to the redistribution of airflow caused by large orifices in the center, followed by the elimination of sidewall effects, the two-size-orifice distributor with 4mm inner orifices and 2mm outer orifices can improve the fluidization quality compared with other distributors and further promote the density segregation process of coal particles in the bed (ash separation degree Sash=21.62%). Finally, the coal particles are separated in a fluidized bed with the abovementioned two-size-orifice distributor. The yield of clean coal products is 54.83% with an ash content of 20.96%, while the yield of gangue is 45.17% with an ash content of 30.77%. Moreover, the possible error is as low as 0.10g/cm3, indicating the good separation effect of the gas–solid separation fluidized bed with the two-size-orifice distributor.

Gas–Solid Distribution Theory in a Pulsed Fluidized Bed Based on the Intermediate Phase

Fluidized bed technology is widely used in chemical industries. The introduction of pulsating energy into a traditional fluidized bed can effectively reduce the generation of bubbles and improve the fluidization quality. The accuracy of gas–solid distributions has a significant influence on the density control of fluidized beds. Here, a gas–solid distribution model and bed expansion prediction model were established with the wake taken as the intermediate phase to make up for the lack of a gas–solid distribution theory in a pulsed fluidized bed. The correlation coefficient of the theoretical model was validated using data obtained from collapse experiments. The linear fitting correlation between the bed expansion height H(p) and correction coefficient Y is quite good. The error of the modified model of the bed expansion ratio was found to be within 20%, which enables it to provide theoretical guidance for industrial applications of pulsed fluidized beds.

MP-PIC simulation of the effects of spent catalyst distribution and horizontal baffle in an industrial FCC regenerator. Part I: Effects on hydrodynamics

Improving distribution uniformity of spent catalyst and adding horizontal baffles are two effective measures to improve the regeneration performance of a fluid catalytic cracking (FCC) unit. In this study, an industrial coaxial compact FCC regenerator is simulated using a Eulerian- Lagrangian multi-phase particle in cell (MP-PIC) method. By using the energy-minimization multi-scale (EMMS) drag model based on turbulent flow regime, the MP-PIC simulation predicts the typical solids fraction profile which is in good agreement with industrial data. The Crosser grid (a typical horizontal baffle) is successfully constructed with the help of “virtual baffles” in simulation. The simulation results show that, after adding Crosser grid (a new horizontal fluidized bed baffle by our group), the bed height increases slightly, the lateral mal-distribution index of solids decreases and the descending flux of spent catalysts decreases significantly. The distribution uniformity of spent catalyst distribution along the bed cross section is more uniform when spent catalyst particles are distributed more uniformly. The presence of gas cushion beneath the Crosser grid allows it to act as a pseudo gas distributor, eliminating gas channeling and decreasing zones of low fluidization quality. The rising bubbles are absorbed by the gas cushion and new small bubbles are generated above the Crosser grid, thereby strengthening the gas–solid contact. The guiding vanes of Crosser grid accelerate the lateral movement of particles. The Crosser grid also proves its stronger suppression on the axial back-mixing of solids.

Gas-solid mixing characteristics of Geldart B particles in a fluidized bed with different height-to-diameter ratios

Under different height-to-diameter ratios (H/D), the gas-solid mixing characteristics in a fluidized bed filled with Geldart B were studied employing the Eulerian-Eulerian two-fluid model. Researches showed that with the H/D increased, the larger bubbles were generated and significantly affected the gas-solid mixing process. And at H/D=1.5, the radial particle velocity distribution had a relatively smaller fluctuation at different axial heights and a higher particle fluidization quality was obtained. Therefore, it can be concluded that under given conditions, a proper H/D is essential for obtaining a good gas-solid mixing in a fluidized bed.

Experimental investigation of axial Solid concentration distribution in fluidized bed

The axial solid concentration distributions were measured by using pressure inspection instrument in a glass bead fluidized bed. Set 1-3 belong to single size distribution and Set 4-5 have wide size distribution, respectively. The change trend of axial solid concentration distributions were investigated under different superficial gas velocities, particle size and particle density. The results showed that, with increasing superficial gas velocity, the solid concentrations in dense region decreased, but increased in dilute region. The glass bead particles whose particle size and particle density were smaller had good fluidization quality. It was also found that the joining of fine particles can significantly change the flow characteristics of the fluidized solid particles.

Experimental and numerical investigations on the hydrodynamics of gas-solid fluidized bed with an inclined agitator

The effect of inclined agitation on the fluidization quality of a gas-solid fluidized bed is experimentally and numerically investigated. The pressure characteristics are characterized by the standard deviation of pressure drop and power spectra. The particle velocity, solid volume fraction and granular temperature distributions are investigated by numerical modeling. It is found that inclined agitation enhances the gross circulation of solid particles and enlarges the affect region of the agitator, improving the gas-solid fluidization quality. The increase in the agitation speed leads to higher frequency of collisions and more activity of particles, resulting in decreases of bubble sizes and a more homogeneous solid volume fraction distribution. Wide-blade agitator can also improve the fluidization performance.

Enhanced fluidization of group A particles modulated by group C powder

Geldart Group A powders are utilized in various industrial processes because of their good fluidization quality, which is closely related to fine content (≤ 45 μm). This work systematically investigated the effect of fine powders (≤ 20 μm) as additives on the fluidization quality of Group A powders. Three types of additives, Coal-15, GB-6, and SiO2-5 were added into the base powder FCC-76 (Group A) in various volume fractions. Among them, the addition of SiO2-5 showed a significant improvement on the fluidization quality of Group A powder, exhibiting lower minimum fluidization velocity and higher bed expansion, while the addition of Coal-15 slightly improved the fluidization quality. The addition of a high-volume fraction of GB-6 would turn Group A into Group C/A, exhibiting some fluidization characteristics of Group C particles. Overall, the fluidization advancement of Group A powders modulated by Group C additives has advantages for industrial processes, especially for gas-phase catalytic reactions.