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.

Estimation of Bed Expansion and Separation Density of Gas–Solid Separation Fluidized Beds Using a Micron-Sized-Particle-Dense Medium

Coal is the dominant energy resource in China. With the Chinese policy of committing to reducing peak carbon dioxide emissions and achieving carbon neutrality, coal separation has recently become a hot topic, especially the fluidized separation of fine particles. In this study, micron-sized particles were introduced to ameliorate the properties of the traditional fluidized bed. The expansion characteristics of the micron-sized-particle-dense medium were explored. A bed expansion prediction model of the micron-sized-particle-dense medium was established, and the prediction error was about 10%, providing a theoretical basis for understanding the distribution characteristics of the bed. This model also helped predict the bed density in the presence of a micron-sized-particle-dense medium, and the prediction accuracy was between 85% and 92%, providing a theoretical basis for selecting and popularizing fluidized beds for industrial separation.

Segregation and intermixing in polydisperse liquid-solid fluidized beds: A multi-fluid model validation study

Multifluid model (MFM) simulations have been carried out on liquid-solid fluidized beds (LSFB) consisting of binary and higher-order polydisperse particle mixtures. The role of particle-particle interactions was found to be as crucial as the drag force under laminar and homogenous LSFB flow regimes. The commonly used particle-particle closure models are designed for turbulent and heterogeneous gas-solid flow regimes and thus exhibit limited to no success when implemented for LSFB operating under laminar and homogenous conditions. A need is perceived to carry out Direct Numerical Simulations of liquid-solid flows and extract data from them to develop rational closure terms to account for the physics of LSFB. Finally, a recommendation flow regime map signifying the performance of the MFM has been proposed. This map will act as a potential guideline to identify whether or not the bed expansion characteristics of a given polydisperse LSFB can be correctly simulated using MFM closures tested.

Design and Investigation of a 3D-Printed Micro-Fluidized Bed

Micro-fluidized bed has aroused much attention due to its low-cost, intensified-process and fast-screening properties. In this paper, a micro-fluidized bed (15 × 15 mm in cross-section) was designed and fabricated with the use of the stereolithography printing technique, for the investigation of bubbles’ hydrodynamics and comparison of the solids (3D-printed particles VS fungal pellets) fluidization characteristics. In a liquid–gas system, bubble flow regime started from mono-dispersed homogeneous regime, followed by poly-dispersed homogeneous regime, transition bubble regime and heterogeneous bubble regime with increasing gas flowrates from 3.7 mL/min to 32.7 mL/min. The impacts from operating parameters such as gas flowrate, superficial liquid velocity and gas sparger size on bubble size, velocity and volume fraction have been summarized. In liquid–solid fluidization, different solid fluidization regimes for both particles bed and pellets bed were identified. From the bed expansion results, much higher Umf of 7.8 mm/s from pellets fluidization was observed compared that of 2.3 mm/s in particles fluidization, because the hyphal structures of fungal pellets increased surface friction but also tended to agglomerate. The similar R–Z exponent n (5.7 and 5.5 for pellets and particles, respectively) between pellets and particles was explained by the same solid diameter, but much higher Ut of 436 µm/s in particles bed than that of 196 µm/s in pellets bed is a consequence of the higher density of solid particles. This paper gives insights on the development of MFB and its potential in solid processing.

Energy and Water Savings during Backwashing of Rapid Filter Plants

This paper describes an analysis of the effects of adjusting the intensity of filter backwash to the water temperature. The consequences of the lack of such adjustment for the life of filter beds, the amount of water used for backwashing, the amount of energy used for backwashing and the quality of the first filtrate are presented. In order to determine the losses and profits resulting from controlling the intensity of backwash water depending on its temperature, an analysis was carried out at a water treatment plant in southern Poland. Laboratory measurements were used to determine the granulation and specific gravity of sand grains filling the filtration beds. On the basis of measurements on a semi-technical scale, the magnitudes of filter bed expansion were determined for average monthly wash water temperatures. They were first calculated from the Richardson–Zaki equation, using different formulae for the value of the exponent of the power in this equation. Due to significant differences in the density and shape of grains covered with a permanent deposit after several years of filter operation, a satisfactory match between the formulae known from the literature and the results of expansion measurements was not obtained. Therefore, an new formula for the bed expansion was developed based on the Richardson–Zaki equation. A good fit of this formula to the experimental results was obtained. Monthly average values of water temperature were compiled, and on this basis the required amount of backwash water and energy was computed. The computations were made for 25% of fluidized bed expansion. Possible energy and water savings were estimated, as well as further gains from keeping the required expansion of the porous bed constant regardless of the wash water temperature.

Hydrodynamics of Turbulent Bed Contactor with Non Newtonian Liquids

Little information is available in literature in terms of the hydrodynamic characteristics in a turbulent bed contractor [sic] (TBC) with viscous liquids. In this study, the hydrodynamic characteristics in three-phase turbulent bed contactor with counter current flow of air and non-Newtonian liquid was studied and compared with that of Newtonian liquid under consistent conditions. Aqueous solutions of carboxy methyl cellulose (CMC) with apparent viscosities ranged between 5 to 25 cP were used as non-Newtonian liquid. The hydrodynamic parameters iinvestigatedwere: bed pressure drop, minimum fluidization velocity, liquid holdup, bed expansion, and gas holdup. The effect of rheological properties of the CMC aqueous solutions and operating parameters on hydrodynamic characteristics of the TBC were examined. Results showed that increasing CMC concentration increased the net pressure drop across the bed and the liquid holdup, while the gas holdup and bed expansion decreased. At that quoted apparent viscosity range, aqueous solutions of CMC behaved as Newtonian viscous liquids in the TBC.

Hydrodynamics of Turbulent Bed Contactor with Non Newtonian Liquids

Little information is available in literature in terms of the hydrodynamic characteristics in a turbulent bed contractor [sic] (TBC) with viscous liquids. In this study, the hydrodynamic characteristics in three-phase turbulent bed contactor with counter current flow of air and non-Newtonian liquid was studied and compared with that of Newtonian liquid under consistent conditions. Aqueous solutions of carboxy methyl cellulose (CMC) with apparent viscosities ranged between 5 to 25 cP were used as non-Newtonian liquid. The hydrodynamic parameters iinvestigatedwere: bed pressure drop, minimum fluidization velocity, liquid holdup, bed expansion, and gas holdup. The effect of rheological properties of the CMC aqueous solutions and operating parameters on hydrodynamic characteristics of the TBC were examined. Results showed that increasing CMC concentration increased the net pressure drop across the bed and the liquid holdup, while the gas holdup and bed expansion decreased. At that quoted apparent viscosity range, aqueous solutions of CMC behaved as Newtonian viscous liquids in the TBC.

EVALUASI PERFORMANCE REGENERASI MIXED BED POLISHER PADA UNIT DEMINERALISASI

One of the important elements produced from the factory support units is air products. Regional water balance (integration) is important to support factory operations. Raw water is treated in the unit section to produce demin water and further process into Boiler Feed Water (BWF) to produce 80 kg/cm2 pressurized steam in the boiler unit, to meet the specifications as demin water it is necessary to carry out several treatments to remove mineral ions (cations and anions) dissolved in the air. In the mixed bed polisher, there is a resin regeneration process to eliminate saturation of the resin which can no longer bind mineral ions. Regeneration or regent is carried out after the resin pile is saturated which is characterized by an increase in product productivity conductivity with the desired product conductivity target of <0.2 μS/cm at a temperature of 25℃. The purpose of this study was to work or perform a mixed bed polisher, especially during regeneration in the demineralization unit. This research was conducted by making a framework of thought and writing work. The writing stage contains data collection, data processing and data analysis-synthesis, as well as drawing conclusions. Based on this research, the results showed that there was a decrease in the performance of the mixed bed with a bed expansion gain of 80.7% and a resin height of 2.42 m. The number of chemicals used for regeneration is 1170.7 kg consisting of HCL and NaOH so that the flow rate of demin water required to dilute the regenerant is 7,126 m3/h. Keywords: Mixed bad Polisher, Demin water, Resin regeneration.

NUMERICAL SIMULATION AND EXPERIMENTAL STUDY OF INNER FLOW FIELD OF SEED PELLETING PREMIXER IN SPOUTED FLUIDIZED BED

In order to explore the temporal and spatial distribution and motion state of the grains of wheatgrass (Agropyron) seeds and powder in pelleting process, and to find the optimal inlet air speed of pelleting premixer, the pelleting forming mechanism was revealed. Based on Herz-Mindlin contact theory, the contact mechanics model of seed and powder was established. Besides, CPFD software was used to model and simulate the pelleting premixer, and the contact, collision and friction rules among particles were analysed. The simulation and experimental results show that with the increase of inlet wind speed, the bed expansion increases and the unit volume particle concentration decreases, while the air pressure difference only slightly increases. When the inlet wind speed is set at 3.5 m/s, the atomizing nozzle velocity is set at 4.1 m/s, and the seed coating agent flow rate is 0.36 L/min, the particles are suspended due to air isolation, forming a spouted fluidized bed. It is good for seed and powder contact and rapid prototyping. In this time, the pelleting qualified rate was 95.8%. The results provide theoretical basis and technical support for the research of small irregular seeds pelletizing technology.

DEM modelling of swelling of grains

Swelling of grains due to water absorption is ubiquitous in many natural materials and industrial products. Hence, a thorough understanding of grain swelling is of great scientific importance. An experimental investigation can only provide limited information, whereas great insight could be gained from numerical modelling, rigorous numerical models for describing particle swelling are essential. Thus, the objective of this study is to develop and validate a discrete element method (DEM) model for swelling of grains. A first order kinetic model was introduced to describe the swelling of a single grain, and subsequently implemented into the DEM code LIGGGHTS. Model validation was performed by comparing the time evolution of the expansion of a packed bed made of super absorbent polymer (SAP) particles obtained numerically and experimentally. It was demonstrated that the developed model can accurately predict the bed expansion. The validated model was then used to investigate the effect of material properties on the swelling behaviour using rice and SAP as the model materials. It is shown that the swelling depends significantly on material properties, as expected; the expansion of the powder bed made of rice is much lower than that of SAP. The developed model could be further advanced to study consequences of swelling phenomena in granular materials, such as segregation and heat generation.