HOW TO MEASURE THE PARTICLE TRANSLATION AND ROTATION IN A SPOUTED AND FLUIDIZED BED?

Transcription

1 Journal of Chemical Technology V. Idakiev, and L. Metallurgy, Mörl 48, 5, 2013, HOW TO MEASURE THE PARTICLE TRANSLATION AND ROTATION IN A SPOUTED AND FLUIDIZED BED? V. Idakiev, L. Mörl Otto von Guericke University Magdeburg, Faculty of Process and Systems Engineering, Instrumental and Environmental Technology Department (IAUT), Universitätsplatz 2, Magdeburg, Germany vesselin.idakiev@ovgu.de Received 25 May 2013 Accepted 29 July 2013 ABSTRACT In the modeling of fluidized bed processes the knowledge of the movement parameters as well as particle trajectory plays an important role. In this study an innovative magnetic monitoring technique for particle tracking in a fluidized bed was investigated. Moreover, the influence of different bed materials on the movement characteristics of a magnetic marker in a prismatic spouted bed was determined. Using the magnetic monitoring, the location coordinates of an iron ball in bed materials of different density or particle size, by variable air flow rate, were determined and the movement parameters were compared. Results, with respect to the particle movement and particle rotation in a prismatic spouted bed and a flluidized bed are presented. Keywords: fluidization, magnetic monitoring, particle processing. INTRODUCTION The knowledge of the movement processes in fluidized beds is an important prerequisite for the calculation of the pneumatic behaviour of fluidized solids and for modelling of the ongoing processes in the fluidized bed. Therefore, the investigation of the movement parameters as well as particle trajectory plays an important role in the modelling of fluidized bed processes. The determination of the translational and rotational velocity of the single particles allows conclusions to be made about the forces acting on the individual particles and their translational and rotational energy. Numerous particle tracking methods have been proposed [1-4]. Currently, the methods being used for tracking of particles in closed systems are Positron Emission Particle Tracking (PEPT), Radioactive Particle Tracking (RPT), Particle Image Velocimetry (PIV) and Particle Tracking Velocimetry (PTV). Hoffman et al. have reported the use of a medical PET-camera for tracking individual particles in a fluidized bed [5]. However, these particle tracking methods are either expensive and hazardous or capable of only two-dimensional particle tracking. Till now, despite using different measuring techniques it was still not possible to simultaneously measure the particle velocity, its direction in 3D space and the rotation of a particle inside a spouted bed or a fluidized bed.therefore, alternative methods for measurement of particle position and movement parameters are in demand, such as the novel magnetic monitoring technique for tracing a single particle, investigated in this study. The magnetic monitoring has originally been developed for medical purposes to study the human digestive tract [6]. For the first time the method was tested for tracking of particles in a prismatic spouted bed by Gryczka [7] and Mohs et al. [8].Using the magnetic monitoring method, the particle velocity, its direction and also the rotation of a particle can be measured, which is not possible with the known methods. The particle tracking in 2D as well as 3D is possible. The position and orientation of a magnetic doped particle can be determined. From the measured values, the motion parameters for translation and rotation of the particle can be calculated. The aim of the presented research work is to test 445

2 Journal of Chemical Technology and Metallurgy, 48, 5, 2013 the innovative magnetic monitoring system for particle tracking in a prismatic spouted bed and a fluidized bed. To our knowledge, there are no other research works, which focus on the study of the applicability of this technique as a particle tracking method in a fluidized bed. Moreover, the main goals of this study include the following points: - Experimental determination of trajectory parameters of a magnetic marked particle - Calculation of parameters for particle translation and rotation: particle velocity and acceleration; forces affecting particle and stored energy. - Determination of the influence of different layer materials (different density and particle size) and air flow rate on the movement characteristics of a magnetic marker. where r i position vector μ magnetic moment of the marker R position of the dipole. Fig. 1 B presents the magnetic monitoring system with focus on the 12 AMR (Anisotropic Magnetic Resistive) sensors. These sensors are mounted on a base of acrylic glass. The sensors are arranged and calibrated so that they are optimal for the measurement of the magnetic field strength in this installation. Experimental set-up The following experimental program summarizes the used experimental materials and the varied process parameters (Table 1). Several bed materials of different A EXPERIMENTAL Measurement principle The magnetic monitoring technique is based on the measuring the magnetic field strength of a permanent magnet having a magnetic moment μ and on the analysis of the quasi-static stray magnetic field around magnetic dipoles, which can be measured exactly by means of several magnetic field sensors (Fig. 1A). The characteristics of magnetic fields can be illustrated by Maxwell equations [9] which can be written in differential form: δd roth = + δ t δb rote = δt 446 j (1) (2) divd = ρ (3) divb = 0 (4) In these equations H is the magnetic field intensity and D the magnetic displacement density. Values B and E are as follows the magnetic flux density and the electric field intensity, ρ is the electrical charge density and j describes the current density. Knowing the values from these equations Richert et al. [6] give the description of the magnetic dipole filed: H ( r, µ ) i 1 µ π r i = 5 ( µ ( r R) ) ( r R) r i (5) B Fig. 1. (A-B). A. Schematic view of measurement principle. B. Sensor arrangement (12 AMR sensors) on the apparatus.

3 V. Idakiev, L. Mörl Table 1. Experimental program. Fluidized bed Spouted bed Experimental material Plastic ball Wooden ball 10 mm Plastic ball Wooden ball 10 mm Gravel 1; 2; 4; Brass ball Marker Layer Mass [g] Air flow rate [m3/h] Plastic ball with magnet 6mm Wooden ball with integrated magnet 10 mm Plastic ball with integrated magnet Wooden ball with integrated magnet Iron magnetic ball Iron magnetic ball density and particle size are used to investigate the movement characteristics of particles in a prismatic spouted bed and a fluidized bed. For this purpose, the layer mass and the air flow rate are varied, too. These parameters, like material properties and air flow rate, and others such as an equipment design, are the main variables determining the fluid dynamics of a spouted bed or a fluidized bed. A RESULTS AND DISCUSSION The detected marker position in x-y coordinates during the fluidization of particle collective in the investigated fluidized bed and prismatic spouted bed apparatus is shown on Fig. 2(A-D). If the particles are fluidized in a stable operation range of a spouted bed, they move on C B D Fig. 2. (A-D). A. Fluidized bed apparatus. B. Prismatic spouted bed apparatus. Layer mass 500 g; particle size =. Trajectories (x-y) of the marker in the layer material of plastic balls with d = in the fluidized bed (C), and in the spouted bed (D). 447

4 Journal of Chemical Technology and Metallurgy, 48, 5, 2013 Fig. 3 (A-B). A. Translation velocity of the marker in the fluidized bed in dependence of the layer mass: variable parameter - layer mass 250, 750, 850 g; constant parameter - air flow rate 570 m 3 /h. B. Translation velocity of the marker in the in the spouted bed in dependence of the air flow rate: variable parameter - air flow rate: 100, 150, 200 m 3 /h; constant parameter - layer mass 500 g. Fig. 4 (A-B). A. Rotation number of the marker in the fluidized bed in dependence of the air flow rate: variable parameter - air flow rate: 450, 500, 550 m 3 /h; constant parameter - layer mass 300 g. B. Rotation number of the marker in the spouted bed in dependence of the air flow rate: variable parameter - air flow rate: 100, 150, 200 m 3 /h; constant parameter - layer mass 500 g. the typical for the spouted bed cylindrical tracks. The movement of the marker on regular path along the middle profile up through the fountain area to the inclined walls of the spouted bed apparatus is clearly visible (Fig. 2D). In the fluidized bed experiments, the particle trajectory represents the typical paths in a fluidized bed, too. The amount of runaways is minimal. Therefore, using the magnetic monitoring method it was possible to track a single particle in a fluidized bed. In the following figures (Fig. 3 (A-B), Fig. 4 (A- B), and Fig. 5 (A-B)) the movement parameters of the marker, which are determined from the measured values, are presented in regard to their density function and cumulative distribution. As an example, the test series with the plastic ball layer material (d = ) is selected for presenting the results of the translation velocity, rotationnumber and rotation energy. These results illustrate that the air flow rate and the layer mass have a significant 448 influence on the movement characteristics. Results regarding particle translation Fig. 3A shows the translational velocity of the marker in the fluidized bed at different amount of layer mass and a constant air flow rate. The translation velocity is greater in a smaller amount of layer mass. In the spouted bed, with the same amount of layer mass, the translational velocity of the marker varies proportionally to the air flow rate (Fig. 3B). Results regarding particle rotation Fig. 4 shows the rotation number of the marker in the fluidized bed (A) and in the spouted bed (B) in dependence of the air flow rate, at a constant layer mass,. At the highest air flow rate the rotation number of the marker is greatest. This trend is more pronounced in experiments conducted in the spouted bed. While in those, carried

5 V. Idakiev, L. Mörl In conclusion, a novel method for tracking a single particle in a spouted bed as well as in a fluidized bed was successfully applied. For more accurate readings, the marker and solid bed should have the same particle size and similar density. Both, the mean translation velocity and the mean rotation number of markers increase with increasing the air flow rate. The translation velocity decreases with increasing layer mass at constant air flow rate. The variation of air flow rate has a much greater influence on the rotation number and rotation energy in case of prismatic spouted bed compared to fluidized bed. Acknowledgements The authors wish to thank the INNOVENT e.v. Technology Development Jena and the Graduate Scholarship Program of Saxony-Anhalt for their technical and financial support. REFERENCES Fig. 5 (A-B). A. Rotation energy of the marker in the fluidized bed in dependence of the air flow rate: variable parameter - air flow rate: 450, 500, 550 m 3 /h; constant parameter - layer mass 300 g. B. Rotation energy of the marker in the spouted bed in dependence of the air flow rate: variable parameter - air flow rate: 100, 150, 200 m 3 /h; constant parameter - layer mass 500 g. out in the fluidized bed, a certain degree of overlap of the experimental data is observed. The rotation energy of the marker in dependence of the air flow rate, at a constant layer mass, shows similar behaviour (Fig. 5 (A-B)). The highest rotation energy is observed at the highest air flow rate. Again, the obtained dependence is more pronounced in experiments conducted in the spouted bed (B), indicating that the configuration of the apparatus affects the movement parameters of the particles. CONCLUSIONS 1. J. Chaouki, F. Larachi, M. P. Dudukovic, Noninvasive tomographic and velocimetric monitoring of multiphase flows, Industrial and Engineering Chemical Research 36, 1997, M. Olazar, M., M. J. San Jose, S. Alvarez, A. Morales, J. Bilbao, Measurement of particle velocities in conical spouted beds using an optical fiber probe, Industrial and Engineering Chemical Research, 37, 1998, V. Mosorov, D. Sankowski, L. Mazurkiewicz, T. Dyakowski, The bestcorrelated pixels method for solid mass flow measurements using electrical capacitance tomography, Measurement Science and Technology, 13, 2002, J. Link, C. Zeilstra, N. Deen, H. Kuipers, Validation of a discrete particle model in a 2D spout-fluid bed using non-intrusive optical measuring techniques, Canadian Journal of Chemical Engineering, 82, 2004, A.C. Hoffmann, C. Dechsiri, F. Van de Wiel, A. Ghione, H.G. Dehling, Tracking individual particles in a fluidized bed using a medical PET-camera, Proceedings of the 3rd World Congress on Industrial Process Tomography, The Rockies, Alberta, Canada, H. Richert, O. Kosch, P. Goernert, Magnetic monitoring as a diagnostic method for investigating motility in the human digestive system. Magnetism in medicine, Handbook, vol. 2, Weinheim, WILEY-VCH Verlag GmbH & Co. KGaA, 2007, O. Gryczka, Untersuchung und Modellierung der Fluiddynamik in prismatischen Strahlschichtapparaten, Dissertation,

6 Journal of Chemical Technology and Metallurgy, 48, 5, G. Mohs, O. Gryczka, S. Heinrich, L. Mörl, Magnetic monitoring of a single particle in a prismatic spouted bed, Chemical engineering science 64, 2009, J.C. Maxwell, A dynamical theory of the electromagnetic field, Royal Society Transactions, 155, 1865,