Bubble size reduction in electric-field-enhanced fluidized beds

Abstract Fluidized beds are a common form of a chemical reactor, in which a deep layer of solid particles is set in motion by a stream of gas blowing upward. However, the appearance of gas bubbles can significantly limit the selectivity, conversion, and product properties of gas–solid fluidized beds. We present results on the application of low-intensity electric fields in fluidized beds for reducing the bubble size up to 85% while maintaining the free movement of particles so essential to fluidization, at an energy cost as low as 50 W/m 3 . An analysis is presented of the qualitative response of particles to electric fields, including both drift and diffusion of charges. On this basis, the influence of particle size and particle conductivity on the overall dipole moment, and therefore the interparticle forces, is discussed. Experimental results in a two-dimensional bed show the predicted response to changes in particle size, while variations in optimal frequency response can be explained on the basis of particle conductivity. A maximum reduction in bubble diameter of 25% is achieved with small particles ( 77 μ m ) , while for large particles ( 700 μ m ) the bubble diameter can be reduced by as much as 85%.

[1]  Jordan Hristov,et al.  MAGNETIC FIELD ASSISTED FLUIDIZATION – A UNIFIED APPROACH: A SERIES OF REVIEW PAPERS , 2002 .

[2]  Jam Hans Kuipers,et al.  A numerical study of fluidization behavior of Geldart A particles using a discrete particle model , 2004 .

[3]  Alex C. Hoffmann,et al.  The influence of horizontal internal baffles on the flow pattern in dense fluidized beds by X-ray investigation , 1998 .

[4]  G. M. Colver.  An interparticle force model for ac–dc electric fields in powders , 2000 .

[5]  O. Levenspiel.  G/S reactor models—packed beds, bubbling fluidized beds, turbulent fluidized beds and circulating (fast) fluidized beds , 2002 .

[6]  Kurt Liffman,et al.  Onset of cohesive behaviour in gas fluidized beds: a numerical study using DEM simulation , 2001 .

[7]  Roland Clift,et al.  The effect of thin liquid layers on fluidisation characteristics , 1984 .

[8]  C. M. van den Bleek,et al.  Bubble Size Reduction in a Fluidized Bed by Electric Fields , 2003 .

[9]  K Kornelis Rietema,et al.  The effect of interparticle forces on the stability of gas-fluidized beds - I.Experimental evidence , 1990 .

[10]  Wei Wu,et al.  Hydrodynamic characteristics of magnetically stabilized fluidized admixture beds of iron and copper particles , 1999 .

[11]  S. Kaart.  Controlling chaotic bubbles , 2002 .

[12]  J. van Turnhout,et al.  Dielectric study on size effects in polymer laminates and blends , 1998 .

[13]  Filip Johnsson,et al.  Non-intrusive determination of bubble and slug length scales in fluidized beds by decomposition of the power spectral density of pressure time series , 2002 .

[14]  Marc-Olivier Coppens,et al.  Structuring chaotic fluidized beds , 2003 .