•Generalized classification of powders is proposed based on type of fluidization.•Classification is based on interparticle forces acting on particles.•This classification applies to both gas and ...liquid fluidization.•Boundaries in terms of dimensionless interparticle vs. Archimedes number are given.
An extended classification of powders based on their fluidization behavior is proposed for describing their fluidization behavior. This classification takes into account the interparticle forces acting on particles. A diagram is generated, using existing data in the literature, in which the dimensionless interparticle force is plotted against the Archimedes number. At a specific Archimedes number (fixed solid and liquid), type D behavior is expected when dimensionless interparticle force is extremely low. Increasing the interparticle force can change the type of powder to B, then A and finally type C behavior would be encountered at high enough value of dimensionless interparticle force. Clear boundaries were detected between different fluidization behaviors in the proposed diagram. Geldart boundaries, which can be used in the absence of interparticle forces, coincide with the newly proposed boundaries. The absence of an apparent interparticle force can be interpreted as the presence of van der Waals force among particles while no other type of interparticle force is induced on particles. The advantage of considering the boundaries presented in this work is that they can identify the type of fluidization when interparticle forces are significant, which cannot be detected with the extended classifications already available in the literature.
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•Hydrodynamic of gas–solid fluidized beds was studied by RQA and WT methods.•Complex dynamic of fluidized beds were reduced to macro, meso and micro structures.•Effect of gas ...velocity, particle size, settled height and bed diameter were studied.•WT and RQA results were in consistence with each other at all conditions but scale.•Entropy had more consistency with hydrodynamic in scale effect study.
This paper reports the development of nonlinear time series analysis technique based on recurrence quantification analysis (RQA) method to characterize the hydrodynamic of gas–solid fluidized beds and a comparison with the obtained results by wavelet transform (WT) analysis method is made. An experimental work has been carried out at varying conditions, e.g. bed diameter (5, 9, 15cm ID), particle size (150, 300 and 600μm), bed height at aspect ratios (1, 1.5 and 2) and superficial gas velocities (ranging 0.1–1.7m/s). Both methods show that by using larger particles and higher aspect ratios, the contribution of macro structures increases in the system. By increasing the gas velocity, finer structures in the bed first lose their contribution and after passing a transition velocity (of about 0.3, 0.5 and 0.7m/s for sands with mean diameters of 150, 300 and 600μm respectively) their contribution increases again. While the frequency domain analysis is not sensitive to the effect of scale; the RQA method shows an increase in meso structure contribution by increasing of the bed diameter.
This study was carried out to find the optimum clearance (impeller to bottom distance) for Rushton and pitch-blade turbine impellers in a stirred tank bioreactor for improved substrate mixing time ...added at interface, taking advantage of computational fluid dynamics. In this regard, the time needed for a thin layer of liquid, resembling substrate-rich or poor part, getting homogenously dispersed within the tank was calculated. The mixing time calculated in this way is called the surface aeration related mixing time (SARMT). SARMT was calculated using two approaches and was compared with each other. For the pitch-blade turbine impeller, a criterion which guarantees accurate mixing time by simulation was not satisfied, so the SARMT profile against clearance was not achieved. For the Rushton impeller, a general descending order of SARMT against impeller–bottom clearance was observed.
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•Hydrodynamic of a draft tube conical spout fluid bed was studied using pharmaceutical pellets.•Three different hydrodynamic structures were identified in draft tube conical spout ...fluid bed.•Frequency signature for the stable spouting is: (i) 6–9Hz and (ii) 12–15Hz.•The effects of bed height, entrainment zone and distributor hole pitch were discussed.•ΔPd increases with the height of draft tube and distance of the entrainment zone.
Experimental studies of the hydrodynamic performance of the draft tube conical spout-fluid bed (DCSF) were conducted using pharmaceutical pellets. The experiments were carried out in a DCSF consisted of two sections: (a) a conical section with the cross section of 120 mm×250mm and the height of 270mm, (b) a cylindrical section with the diameter of 250mm and the height of 600mm. The flow characteristics of solids were investigated with a high speed camera and a pezoresistive absolute pressure transducer simultaneously. These characteristics revealed different flow regimes in the DCSF: packed bed at low gas velocities, fluidized bed in draft tube at higher gas velocities until minimum spouting, and spouted bed. The stable spouting was identified by the presence of two dominant frequencies of the power spectrum density of pressure fluctuation signature: (i) the frequency band 6–9Hz and (ii) the frequency band 12–15Hz. The pressure drops across the draft tube as well as the annulus measured in order to better recognize the flow structure in the DCSF. It was observed that the pressure drop across the draft tube, the pressure drop across the annulus, and the minimum spouting velocity increase with the increase in the height of draft tube and distance of the entrainment zone, but with the decrease in the distributor hole pitch. Finally, this study provided novel insight into the hydrodynamic of DCSF, particularly minimum spouting and stable spouting in the DCSF which contains valuable information for process design and scale-up of spouted bed equipment.
Gas hold-up (
ɛ
g), sauter mean bubble diameter (
d
32) and oxygen transfer coefficient (
k
L
a) were evaluated at four different alkane concentrations (0.05, 0.1, 0.3 and 0.5
vol.%) in water over ...the range of superficial gas velocity (
u
g) of (1.18–23.52)
×
10
−3
m/s at 25
°C in a laboratory-scale bubble column bioreactor. Immiscible hydrocarbons (n-decane, n-tridecane and n-hexadecane) were utilized in the experiments as impurity. A type of anionic surfactant was also employed in order to investigate the effect of addition of surfactant to organic-aqueous systems on sauter mean bubble diameter, gas hold-up and oxygen transfer coefficient. Influence of addition of alkanes on oxygen transfer coefficient and gas hold-up, was shown to be dependent on the superficial gas velocity. At superficial gas velocity below 0.5
×
10
−3
m/s, addition of alkane in air–water medium has low influence on oxygen transfer coefficient and also gas hold-up, whereas; at higher gas velocities slight addition of alkane increases oxygen transfer coefficient and also gas hold-up. Increase in concentration of alkane resulted in increase in oxygen transfer coefficient and gas hold-up and roughly decrease in sauter mean bubble diameter, which was attributed to an increase in the coalescence-inhibiting tendency in the presence of surface contaminant molecules. Bubbles tend to become smaller with decreasing surface tension of hydrocarbon, thus, oxygen transfer coefficient increases due to increasing of specific gas–liquid interfacial area (
a). Empirical correlations were proposed for evaluating gas hold-up as a function of sauter mean bubble diameter, superficial gas velocity and interfacial surface tension as well as evaluating Sherwood number as a function of Schmidt, Reynolds and Bond numbers.
•A modified two-phase model described the process of gas phase propylene and ethylene copolymerization in a fluidized bed reactor (FBR).•Solid particles entrainment in the FBR is considered in the ...model, as an improvement to the original two-phase model.•A hybrid control strategy (Fuzzy-GMC) was designed to control the reactor temperature.•The simulation results showed that the hybrid controller (Fuzzy-GMC) performs better than either GMC or PID for set point tracking and disturbance rejection with very low overshoot as well as fast and stable response.•The hybrid controller movement was also very stable and fast in terms of both servo and regulatory control, suitable for robust application.
A modified two-phase model is presented to describe the process of gas phase propylene and ethylene copolymerization in a fluidized bed reactor (FBR). Entrainment of solid particles in the FBR is considered in the model, as an improvement to the original two-phase model. Non-linearity of this process makes it difficult to control only by the conventional controllers, such as PID. A hybrid control strategy (a simple designed fuzzy logic controller (FLC) integrated with generic model control (GMC)) was designed to control the reactor temperature. This advanced control system was compared with the GMC and conventional PID controllers. The simulation results showed that the hybrid controller (Fuzzy-GMC) performs better than either GMC or PID for set point tracking and disturbance rejection with very low overshoot as well as fast and stable response. The hybrid controller movement was also very stable and fast in terms of both servo and regulatory control, suitable for robust application.
The local solid flow structure of a bubbling fluidized bed of sand particles was investigated m three different columns to characterize the properties of clusters. The experiments were performed ...using a reflective optical fiber probe. The variations in size, velocity, and void fraction of the clusters due to changes in the superficial gas velocity, particle size, and radial positions were studied. The results indicate that the velocity of the clusters remained unchanged while their size increased as the column diameter increased. In addition, the radial profile of the clusters＇ velocity did not depend on the radial position. The results indicate that larger particles form larger clusters, which move slower.
A comprehensive kinetic model for oxidative coupling of methane (OCM) on Mn/Na2WO4/SiO2 catalyst was developed based on a microcatalytic reactor data. The methane conversion and ethylene, ethane, ...carbon monoxide and carbon dioxide selectivities were obtained in a wide range of operating conditions including 750 < T < 875 deg C, 4 < CH4/O2 < 7.5 and space time between 30 and 160 kg * s/m3 at P = 657 mmHg. The reaction networks of five kinetic models with appropriate rate equation type were compared together. The kinetics rates parameters of each reaction network were estimated using genetic algorithm optimization method. After comparing the reaction networks, the reaction network presented by Stansch et al. was found to best represent the OCM reaction network and was further used in this work. This kinetic network considers both catalytic and gas-phase as well as primary and consecutive reaction steps to predict the performance of the OCM. Comparing the experimental and predicted data showed that presented model has a reasonable fit between the experimental data and the predicted values with average absolute relative deviation of +/- 9.1%.
The dynamic features of an agglomerate bubbling fluidization of nanoparticles were investigated through the analysis of pressure fluctuations. Experiments were carried out in a lab-scale fluidized ...bed at ambient conditions using 10-15 nm silica nanoparticles without any surface modification. Pressure fluctuation signals were processed in both frequency and time-frequency domains to characterize the behavior of various scales of phenomena （i.e.. macro-, meso-, and micro-structures） during fluidization. Due to the aggregation of nanoparticles, three separate broad peaks were observed in the frequency spectra of the pressure signals measured in the bubbling fluidized bed of nanoparticles. A non-intrusive method based on the decoupling of pressure fluctuations recorded simultaneously in the plenum and in the bed was used to determine the approximate size of the bubbles in the bed.
Existence of clusters in dense fluidized beds was investigated by analyzing the time-position data of a tracer obtained in several radioactive particle tracking experiments. It was found that in the ...case of sand particles, more gas passes through the bed as bubbles with increasing the superficial gas velocity and in the case of FCC powder, flow of the gas through the bed as bubbles does not increase in the turbulent fluidization regime. Cluster diameters were estimated from their velocities and found that descending clusters are generally larger than ascending ones and the size of both increases with increasing the superficial gas velocity. Bubble velocities evaluated in this work are in good agreement with the correlations in the bubbling regime of the fluidization available in the literature.
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