Mass transfer from the wall of a column to the fluid in a fluidized bed of inert spherical particles

Abstract

Mass transfer in fluidized beds is an important operation for separation processes. Two effects can be achieved by using fluidized beds in mass transfer processes increasing interface area and relative movement between the phases. These effects are both desirable because they lead to greater process rates. This paper presents an experimental investigation regarding mass transfer from the wall of a column to the fluid in a fluidized bed of inert spherical particles. The experiments were conducted in column 40 mm in diameter with spherical particles 0,8-3 mm in diameter and water as one fluidizing fluid. The method of dissolution of benzoic acid was used to provide very low mass flux. The average wall-to-fluid mass transfer coefficients were determined for two systems: single-phase fluid flow and a fluidized bed of inert particles The measurements encompassed a Reynolds number range from 100-4000 for single-phase flow and 600-4000 in fluidized beds. The mass transfer coefficients for both systems were calculated from weight loss of benzoic acid. The effects of superficial liquid velocity and particle diameter on the mass transfer coefficient were investigated. It was found that mass transfer was more intensive in the fluidized bed in comparison with single phase flow. The best conditions for mass transfer were reached at a minimum fluidization velocity, when the mass transfer coefficient had the greatest value. The experimental data were correlated in the form: jd = f(Re), where jd is the dimensionless mass transfer factor and Re the Reynolds number.

Ispitivan je prenos mase sa zida kolone na fluid u fluidizovanom sloju inertnih sfernih čestica. Eksperimenti su izvršeni u fluidizacionoj koloni prečnika 40 mm, sa sfernim česticama od stakla prečnika 0,8-3 mm i vodom kao fluidizacionim medijumom. Određivan je koeficijent prelaza mase zid kolone-fluidizovani sloj metodom rastvaranja benzoeve kiseline. Ispitivan je uticaj brzine strujanja fluida i karakteristika čestica na koeficijent prelaza mase. Opseg ispitivanih Rejnoldsovih brojeva bio je za strujanje fluida bez čestica (jednofazni tok) od 100-4000, a u fluidizovanom sloju od 600-4000. Rezultati su prikazani kao zavisnosti bezdimenzionog faktora prenosa mase /d od Rejnoldsovog broja Re i Rejnoldsovog broja za česticu Rep. Na osnovu eksperimentalnih rezultata postavljena je korelacija za određivanje koeficijenta prelaza mase u obliku zavisnosti JD = f(Re).