“…When there are solids of different density and/or size present, the net effect of all of these mixing processes can lead to segregation of the different solids into distinct spatial zones. Many previous studies − have examined binary as well as continuous distributions for segregation tendencies. A recent overview of fluid bed segregation summarizes this work and points out that there is still no clear understanding of the details of this process.…”
We report experimental observations of the dynamic behavior
of single, magnetically tagged 3–4 mm particles varying in
density from 0.55 g/cm3 to 1.2 g/cm3 as they
migrate freely in a bubbling air-fluidized bed of 177–250 μm
glass beads of 2.5 g/cm3 density over a range of air flows.
The densities of the tracer particles (made by imbedding small magnets
in wooden particles) were chosen to span a range typical for many
biomass materials and exhibited both segregated and well-mixed behavior.
Using high-speed measurements from externally mounted magnetic probes,
we were able to reconstruct three-dimensional spatial and temporal
information about the tracers’ trajectories over periods of
five minutes. Based on this information, we describe general trends
in how the tracers moved and redistributed themselves as functions
of their density, fluidization air flow, and the overall concentration
of low density particles present. One key finding was that the time
average vertical probability distribution of the tracer particles
locations is consistent with a Weibull distribution. The effective
Weibull parameters appear to vary systematically with the degree of
fluidization and particle density. Also, we observed that temporal
autocorrelations in the vertical position of the tracer particles
vary systematically with fluidization intensity and reveal important
information about the dominant bed circulation time scales. Our results
suggest that it may be possible to develop relatively simple statistical
models or correlations for describing the spatial distribution and
circulation of mm sized particles in bubbling beds of this type. Such
tools should be useful for simulating some types of fluidized biomass
processing and for validating kinetic-theory models of fluidized bed
systems.
“…When there are solids of different density and/or size present, the net effect of all of these mixing processes can lead to segregation of the different solids into distinct spatial zones. Many previous studies − have examined binary as well as continuous distributions for segregation tendencies. A recent overview of fluid bed segregation summarizes this work and points out that there is still no clear understanding of the details of this process.…”
We report experimental observations of the dynamic behavior
of single, magnetically tagged 3–4 mm particles varying in
density from 0.55 g/cm3 to 1.2 g/cm3 as they
migrate freely in a bubbling air-fluidized bed of 177–250 μm
glass beads of 2.5 g/cm3 density over a range of air flows.
The densities of the tracer particles (made by imbedding small magnets
in wooden particles) were chosen to span a range typical for many
biomass materials and exhibited both segregated and well-mixed behavior.
Using high-speed measurements from externally mounted magnetic probes,
we were able to reconstruct three-dimensional spatial and temporal
information about the tracers’ trajectories over periods of
five minutes. Based on this information, we describe general trends
in how the tracers moved and redistributed themselves as functions
of their density, fluidization air flow, and the overall concentration
of low density particles present. One key finding was that the time
average vertical probability distribution of the tracer particles
locations is consistent with a Weibull distribution. The effective
Weibull parameters appear to vary systematically with the degree of
fluidization and particle density. Also, we observed that temporal
autocorrelations in the vertical position of the tracer particles
vary systematically with fluidization intensity and reveal important
information about the dominant bed circulation time scales. Our results
suggest that it may be possible to develop relatively simple statistical
models or correlations for describing the spatial distribution and
circulation of mm sized particles in bubbling beds of this type. Such
tools should be useful for simulating some types of fluidized biomass
processing and for validating kinetic-theory models of fluidized bed
systems.
“…The complete fluidization velocity (U fc ), defined as the minimum air velocity at which all the particles are suspended (Tannous et al, 1998;Gauthier et al, 1999), was determined for each condition. To ensure that all the particles were suspended, particularly in the experiments involving a binary particle size distribution, the air fluidization velocity was kept at a value 10% above U fc .…”
-In this work the effects of particle size distribution on the dynamics and segregation patterns in fluidized, vibrated and vibrofluidized beds were investigated. A binary particle size distribution and a reference one composed of glass spheres with a mean Sauter diameter of 2.18×10 -3 m were tested. The experimental setup consisted basically of a circular glass chamber with a height of 0.50 m and a diameter of 0.114 m, operated in the fluidized bed mode ( = 0.00), in either vibrated or vibrofluidized bed modes ( = 2.00). The pressure drops in the fluidized and vibrofluidized beds were not significantly affected by the binary particle size distribution. Well-defined segregation patterns occurred in fluidized and vibrated beds with small particles concentrating at the top and large particles at the bottom in the first situation and the reverse in the second one. Segregation patterns in vibrofluidized beds depended on the values of vibration parameters. Segregation in vibrofluidized and vibrated beds was minimized by operating at a high amplitude of vibration.
“…Depending on the kinds of biomass particles, these determinations can be distinct, mainly referring to the segregation velocity (gray patterned area). The approach was proposed firstly by Punčochář, Drahoš, Čermák, and Selucký [34] for homogeneous particles, and later applied to polydispersed particles [35] and to binary mixtures [9]. In this case, the characteristic velocities are determined according to the inflections in the curve schematized in Fig.…”
Decease of natural resources and increase of price of fossil fuels at growing energy consumption, toughening of ecological standards and necessity of the increase of the level of energetics diversification motivates mankind to more wide usage of renewable energy resources including the solid fuel of biological origin. The potential of biofuel usage is rather considerable because the energy equivalent of the biomass harvest on the land exceeds the worldwide energy consumption several times as much. The biomass application as a renewable fuel is already a reality worldwide with the development of policies and technologies that turn viable the transformation of biomass into energy. The aims of this work is to present a literature experimental review on the studies concerning to the use of fluidized beds taking into account their design and scale-up. Initially, the usual solid particle terminology and some important biomass properties are presented. A brief description of conversion technologies and the fluidization phenomena are introduced, followed by an explanation of the different experimental techniques. The characteristic velocities (initial, apparent, of segregation, and complete) are discussed based on different biomass properties, as well as a number of empirical correlations for these velocities are described. Finally, some considerations are made about characteristic bed porosities (apparent and complete) and bed expansion. Based on the literature analysis, an improvement has been done on the understanding of the biomass fluidization phenomena, however, further research is needed to comprehend the effect of biomass characteristics on the bed operational parameters, besides more accurate and general correlations must be developed to improve these technologies.
For citation:
Tannous K., De Mitri A.G., Mizonov V. Experimental study of fluid dynamic behavior of biomassparticles in fluidized beds: a review. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2018. V. 61. N 9-10. P. 4-14
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