Radmila Garic-Grulovic

Determination of non-spherical particle terminal velocity using particulate expansion data

Abstract A new method is proposed for the determination of the terminal velocity of non-spherical particles and compared with experimental data. The method is based on particulate expansion data of fluidized bed and variational model for calculating fluid–particle interphase drag coefficient. Other methods require knowledge of the particle shape, a parameter that is not easy to obtain for real materials. We use pressure drops data in packed bed for indirect determination of particle shape factor which depends on the reliability of coefficients in the Ergun equation. Our data, however, show that these coefficients are system-specific. The proposed method for the determination of non-spherical particle settling velocity in liquid as well as extrapolation to system gas-particles gives results which are in good agreement with experimental data. The method is restricted to particles which can be fluidized particulately by liquid.

Drying of Slurries in Fluidized Bed of Inert Particles

Abstract A fluid bed dryer with inert particles was used for drying of slurries. Experiments were performed in a cylindrical column 215 mm in diameter and 1200 mm in height with glass spheres as inert particles. Slurries of Zineb fungicide, copper hydroxide, calcium carbonate, and pure water were used as the feed material. The effects of operating conditions on dryer throughput and product quality were investigated. Main performance criteria, i.e., specific water evaporation rate, specific heat consumption, and specific air consumption, were quantified. Temperature profile along the bed was mapped, and nearly isothermal conditions were found due to thorough mixing of the particles. The material hold-up and residence time were determined. Simple heat and mass balances predict the dryer performance quite well.

Mass transfer and fluid flow visualization in packed and fluidized beds by the adsorption method

Mass transfer coefficient (jD) between fluid and column wall in liquid packed and fluidized beds of spherical inert particle has been studied experimentally using adsorption method. Experiments were conducted in column 40 mm in diameter for packed and fluidized beds. In all runs mass transfer rates were determined in presence of spherical glass particles 2.06 mm in diameter. This paper introduced adsorption method as very suitable method for studies of mass transfer and for fluid flow visualization. The adsorption method is based on the dynamic adsorption of an organic dye onto a surface covered with a thin layer of a porous adsorbent. Local and average mass transfer coefficients were determinated from the surface color intensity of the foils of silica gel. Correlation jD = f(Re) was derived using mass transfer coefficients data.

Hydrodynamics and Mass Transfer in Heterogeneous Systems

Research of transport phenomena in liquid – particles systems, in past years, had a more theoretical then practical importance (Coudrec, 1985; Lee et al., 1997; Schmidt et al., 1999). For industrial use, especially with fast development of bio and water cleaning processes, better knowing of these systems become more important. An industrial application of these systems requires determination of transfer characteristics, especially mass transfer. Frequently mass transfer is the rate determining step in the whole process. However, in the real systems, it is not always easy to differentiate the limitation due to the mass transfers from that due to the hydrodynamic. Mass transfer in liquid-solid packed and fluidized beds has been widely investigated in terms of particle–fluid mass transfer by dissolution, by electrochemical and by ion-exchange methods (Damronglerd et al. 1975; Koloini et al. 1976; Dwivedi & Upadhyay, 1977; Chun & Couderc, 1980; Kumar & Upadhyay, 1981; Rahman & Streat, 1981; Yutani et al. 1987). Some of the results of mass transfer in packed and fluidized beds have been obtained as the transfer between an immersed surface and the liquid (Riba et al. 1979; Boskovic et al. 1994; Boskovic-Vragolovic, et al., 1996&2005). Liquid fluidization of particulate solids has a history which predates the now more commonly applied gas fluidization. The broad range of operations to which liquid fluidization has found applications are: classification of particles by size and density, a special case being sink-and-float separation by density; backwashing of granular filters and washing of soils; crystal growth; leaching and washing; adsorption and ion exchange; electrolysis with both inert and electrically conducting fluidized particles; liquid-fluidized bed heat exchangers and thermal energy storage; and bioreactors. Fluidized-bed bioreactors, which have received much attention during the past thirty years, are usually characterized by the catalytic use of enzymes or microbial cells that are immobilized by attachment, entrapment, encapsulation or self-aggregation. The most common application of such bioreactors is probably in wastewater treatment and, as in the case of the other operations mentioned above, liquid fluidization must in each case be weighed against competing schemes for achieving the same objective before it is adopted commercially (Epstein, 2003). In contrast to fluidized beds data, there are no published data on mass transfer in vertical and horizontal hydrotransport of particles.

Experimental study on the ozone absorption accompanied by instantaneous chemical reaction

ABSTRACT This work deals with gas absorption accompanied by chemical reaction in a liquid phase. Ozone absorption in potassium indigotrisulfonate solution was investigated in a batch bubble column. Enhancement factor for absorption accompanied by instantaneous chemical reaction in the liquid phase was experimentally determined, as a ratio of the volumetric mass transfer coefficient for the absorption accompanied by reaction to that for pure physical absorption. The influence of (a) the initial concentration of the solute from liquid phase and (b) the ozone concentration in gas phase on the enhancement factor were experimentally examined. The absorption accompanied by instantaneous chemical reaction is a diffusion-controlled process, whose rate depends upon the diffusivities of the absorbing gas and the solute in liquid phase. The influence of these diffusivities was found to be more significant for lower values of the enhancement factor. The rate of ozone absorption was followed by the time change of the solution color, using new method based on the computer program SigmaScan Pro 5 (Systat Software, Inc., San Jose, CA, USA). This investigation is a contribution to the prediction of the ozone consumption in wastewater treatment, in cases when ozone instantaneously reacts with substances present in water.

Prevention and control of dimethylamine vapors emission: Herbicide production plant

The widely used herbicide, dimethylamine salt of 2,4-dichlorophenoxy acetic acid (2,4-D-DMA), is usually prepared by mixing a dimethylamine (DMA) aqueous solution with a solid 2,4-dichlorophenoxy acetic acid (2,4-D). The vapors of the both, reactants and products, are potentially hazardous for the environment. The contribution of DMA vapors in overall pollution from this process is most significant, concerning vapor pressures data of these pollutants. Therefore, the control of the air pollution in the manufacture and handling of methylamines is very important. Within this paper, the optimal air pollution control system in preparation of 2,4-D-DMA was developed for the pesticides manufacturing industry. This study employed the simple pollution prevention concept to reduce the emission of DMA vapors at the source. The investigations were performed on the pilot plant scale. To reduce the emission of DMA vapors, the effluent gases from the herbicide preparation zone were passed through the packed bed scrubber (water scrubbing medium), and the catalytic reactor in sequence. The end result is a substantially improved air quality in the working area, as well as in the urbanized areas located near the chemical plant.